A coated modified high-voltage lithium cobalt oxide cathode material, a preparation method thereof and a lithium ion battery

Abstract

The application discloses a coated modified high-voltage lithium cobaltate positive electrode material, a preparation method thereof and a lithium ion battery. The coated modified high-voltage lithium cobaltate positive electrode material comprises a core and a coating layer arranged on the surface of the core, the core is lithium cobaltate, and the coating layer comprises a Li4P2O7-PrPO4 composite. The application realizes the interface stabilization of the high-voltage lithium cobaltate positive electrode material under the condition of 4.7 V by constructing a Li4P2O7-PrPO4 composite coating layer on the surface of the lithium cobaltate. The composite coating layer has ion conductivity and chemical inertia, and can effectively inhibit electrolyte decomposition, transition metal dissolution and lattice oxygen loss. The prepared material has higher capacity retention rate and cycle stability under high voltage, and significantly improves the electrochemical performance and safety of the high-energy-density lithium cobaltate positive electrode.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and particularly relates to a coated and modified high-voltage lithium cobalt oxide cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Driven by the urgent global need for energy transition and sustainable development, lithium-ion batteries, with their significant advantages such as high energy density, long cycle life, low self-discharge rate, and environmental friendliness, have become a core energy storage technology in portable electronic devices, electric vehicles, and large-scale energy storage systems. As the performance requirements of related applications continue to increase, continuously optimizing the overall performance of lithium-ion batteries, especially energy density and cycle stability, has become a key research goal and core challenge in this field.

[0003] Among the many factors that determine the performance of lithium-ion batteries, the cathode material plays a crucial role, directly determining the upper limit of the battery's energy density and long-term cycle stability. Currently, commercially used cathode materials mainly include layered oxides (such as lithium cobalt oxide LiCoO2, lithium nickel cobalt manganese oxide NCM, and lithium nickel cobalt aluminum oxide NCA), spinel-type lithium manganese oxide (LiMn2O4), and olivine-type lithium iron phosphate (LiFePO4).

[0004] Lithium cobalt oxide (LiCoO2), as the earliest layered cathode material to achieve large-scale commercialization, has long dominated the high-end consumer electronics market due to its advantages such as high theoretical capacity (~274 mAh / g), high compaction density, and stable electrochemical performance. However, conventional lithium cobalt oxide (operating voltage typically ≤4.45 V vs. Li...) ＋ In a deeply delithiated state (high state of charge, SOC), lithium cobalt oxide (Li₂O₃) is prone to crystal structure instability (such as irreversible phase transitions) and intensified surface and interface side reactions (such as electrolyte decomposition and dissolution of transition metal ions). This results in limited actual reversible capacity (typically only about 140-155 mAh / g is released) and significantly reduced cycle stability. These problems severely restrict the full realization of the performance of lithium cobalt oxide materials.

[0005] To fully tap the energy density potential of lithium cobalt oxide, raising the charging cutoff voltage to above 4.5 V (such as 4.6 V, 4.7 V, or even higher) has become an important technological path. Existing modification methods and their limitations: Regarding the stability issues of lithium cobalt oxide (including high-voltage types), existing technologies mainly employ two strategies: elemental doping and surface coating. Introducing heterogeneous metal ions (such as Al, Mg, Ti, La, etc.) into the crystal lattice aims to stabilize the crystal structure, suppress phase transitions, and reduce oxygen loss. However, the doping effect is limited by the type, concentration, and uniformity of element distribution, and its improvement effect on the severe interface problems under high voltage is limited. Coating modification, on the other hand, constructs a physical / chemical barrier on the surface of lithium cobalt oxide particles, which is the most direct and effective means of isolating the positive electrode active material from the electrolyte and suppressing interfacial side reactions. The coating layer can significantly improve the interfacial stability of the material under high voltage and reduce electrolyte decomposition and transition metal dissolution, but traditional coating technologies still have bottlenecks that urgently need to be addressed. Especially under extreme conditions of 4.7 V or even higher voltages, more stringent requirements are placed on the composition design, microstructure control (such as thickness, coverage, and porosity) and fabrication process of the coating layer.

[0006] Therefore, developing a novel preparation method for constructing an ultrathin, uniform, dense, and tough coating layer with excellent compatibility with high-voltage lithium cobalt oxide substrate is of great scientific significance and engineering application value for fully leveraging the potential of 4.7 V high-voltage lithium cobalt oxide and achieving a synergistic improvement in high energy density and long cycle life. Summary of the Invention

[0007] The purpose of this invention is to provide a coated and modified high-voltage lithium cobalt oxide cathode material, its preparation method, and a lithium-ion battery. By constructing a Li4P2O7-PrPO4 composite coating layer on the surface of the lithium cobalt oxide cathode material, the surface structure stability of lithium cobalt oxide is improved, the near-surface lithium-ion transport rate is enhanced, thereby improving the rate performance and cycle stability of lithium cobalt oxide, and thus improving the electrochemical performance at a cutoff voltage of 4.7 V.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a coated and modified high-voltage lithium cobalt oxide cathode material, comprising a core and a coating layer disposed on the surface of the core, wherein the core is lithium cobalt oxide and the coating layer comprises a Li4P2O7-PrPO4 composite.

[0010] Based on the above technical solutions, this invention addresses the severe surface side reactions and decreased interface stability of lithium cobalt oxide during high-voltage cycling. By constructing a composite coating layer containing PrPO4 and Li4P2O7, not only can PrPO4 stabilize the surface crystal structure and construct a stable CEI layer, but the fast ion conductor composed of Li4P2O7 can also improve the rate performance of lithium cobalt oxide. The inventors have discovered that, compared to doping lithium cobalt oxide, the cathode material modified by applying Pr to the surface coating layer exhibits superior electrochemical performance.

[0011] According to embodiments of the present invention, the mass ratio of the core to the coating layer is 1:(0.01-0.05), preferably 1:(0.02-0.05), more preferably 1:0.02 or 1:(0.04-0.05), including but not limited to 1:0.01, 1:0.02, 1:0.03, 1:0.04 or 1:0.05. The inventors have found that when the mass ratio of the core to the coating layer is too low, it cannot maximize the stability of the lithium cobalt oxide surface; conversely, when the coating layer ratio is too high, it is not entirely beneficial for improving cycle stability.

[0012] According to embodiments of the present invention, in the Li4P2O7-PrPO4 composite, the molar ratio of Li4P2O7 to PrPO4 is 1:(1.5-2.5), including but not limited to 1:1.5, 1:2, and 1:2.5. In a preferred embodiment of the present invention, the molar ratio (Li4P2O7:PrPO4) in the Li4P2O7-PrPO4 composite is approximately 1:2, i.e., approximately 30 wt% Li4P2O7 / 70 wt% PrPO4. Approximately 70 wt% PrPO4 forms a continuous and dense protective layer, suppressing oxidation / side reactions; approximately 30 wt% Li4P2O7 is sufficient to form ion-conducting channels or local Li dissolution points in the protective layer, avoiding the negative effects of "complete isolation." If the PrPO4 phase ratio is too high, although PrPO4 is chemically stable, its electronic / ionic conductivity is poor, and excessive thickness will significantly increase the electrode internal resistance, leading to capacity loss or rate reduction. If the proportion of Li4P2O7 is too large, although it is beneficial to Li ion transport, it has a weak ability to inhibit oxidation side reactions and Co dissolution under high voltage, resulting in a decrease in cycle stability.

[0013] In a second aspect, the present invention provides a method for preparing the coated and modified high-voltage lithium cobalt oxide cathode material as described in any of the preceding claims, comprising the following steps:

[0014] S1. After mixing lithium cobalt oxide powder and water, ozone is introduced for treatment. After treatment, a surfactant is added to obtain a wet suspension of lithium cobalt oxide.

[0015] S2. Add the template agent to the system obtained in step S1 for processing to obtain a lithium cobalt oxide water-in-oil suspension emulsion;

[0016] S3. Precursor solution A containing praseodymium source, lithium source and chelating agent and precursor solution B containing phosphate source are respectively added to the lithium cobalt oxide oil-in-water suspension emulsion to obtain the emulsion system.

[0017] S4. Add solvent to the emulsion system to break the emulsion and separate and collect the powder.

[0018] S5. The powder is calcined to obtain the coated and modified high-voltage lithium cobalt oxide cathode material.

[0019] Based on the above technical solutions, this invention employs an emulsion template method to construct a Li4P2O7-PrPO4 composite coating layer on the surface of lithium cobalt oxide cathode material, effectively improving the electrochemical performance of lithium cobalt oxide at a high voltage of 4.7 V. The principle of synthesizing Li4P2O7-PrPO4-coated lithium cobalt oxide using the emulsion template method is as follows: first, ozone is used to activate the surface of lithium cobalt oxide to generate active groups; then, a template is added to its aqueous suspension, and ultrasonic stirring is performed to form an oil-in-water emulsion of lithium cobalt oxide. PLA-PEG stabilizes the interface and constructs the reaction space. Subsequently, a PrPO4-containing emulsion is slowly added... 3+ Li + Chelating precursors and PO4 3- The precursor is directionally deposited on the surface of lithium cobalt oxide under confinement. After demulsification with ethanol and drying to remove organic matter, the precursor is decomposed and undergoes a solid-phase reaction in two steps of calcination, ultimately forming a dense composite coating layer. The emulsion template effectively avoids random precipitation of the precursor and ensures uniform coating.

[0020] According to an embodiment of the present invention, the ratio of lithium cobalt oxide powder to water is (1-5) g: 50 mL, including but not limited to 2 g: 50 mL.

[0021] Before introducing ozone in step S1, the mixture of lithium cobalt oxide powder and water is subjected to ultrasonic treatment, such as ultrasonication at 200W for 10 minutes. This ultrasonication step can clean the lithium cobalt oxide powder.

[0022] The concentration of ozone in the mixture of lithium cobalt oxide powder and water is 5–10 mg / L, such as 10 mg / L. The ozone treatment time is 10–30 min. Ozone decomposes in water to produce hydroxyl radicals, which can slightly oxidize the surface of lithium cobalt oxide, increase the surface hydroxyl density, and facilitate the adsorption of oxygen-containing anions (phosphate) and subsequent precipitation reactions.

[0023] The surfactant is EDTA, and the mass ratio of lithium cobalt oxide to the surfactant is 1:(0.02~0.05), such as 1:0.05. The surfactant can reduce the liquid-solid interfacial tension, making the precursor solution easier to wet the surface of lithium cobalt oxide and promoting uniform nucleation of the coating layer.

[0024] According to an embodiment of the present invention, the template agent is PLA-PEG. The template agent is added in the form of an organic solution of PLA-PEG, with dichloromethane as the solvent, wherein the mass of PLA-PEG in each 20 mL of dichloromethane is 0.1–0.2 g, including but not limited to 0.2 g. As an example, the molecular weight of PLA-PEG is 5000. The feed rate of the template agent in the system obtained in step S1 is 0.5–1 mL / min, such as 0.5 mL / min; the treatment in step S2 is carried out under ultrasonic and stirring conditions, such as ultrasonication at 300 W and stirring at 400 rpm for 30 min.

[0025] According to embodiments of the present invention, the praseodymium source is selected from any one of praseodymium acetate, praseodymium nitrate, and praseodymium chloride. The lithium source is selected from any one of lithium acetate, lithium oxalate, and lithium nitrate. The molar ratio of the praseodymium source to the lithium source, calculated as Pr:Li, is (0.375–0.625):1, including but not limited to 0.375:1, 0.5:1, and 0.625:1, and can be adjusted according to the molar ratio of Li4P2O7 and PrPO4 in the composite. The chelating agent is citric acid. The molar ratio of the chelating agent to the metal ions (Pr and Li) in the praseodymium source and the lithium source is 1:1. The purpose of adding the chelating agent is to prevent uncontrolled bulk precipitation, forcing the precipitation reaction to occur only on the surface of lithium cobalt oxide, thereby forming a dense, uniform, and firmly bonded nanoscale coating layer.

[0026] The phosphoric acid source is selected from one or more of ammonium dihydrogen phosphate and phosphoric acid. The molar ratio of the phosphoric acid source to the praseodymium source, calculated as P:Pr, is (1.8–2.3):1, including but not limited to 2.3:1, 2:1, and 1.8:1, and can be adjusted according to the molar ratio of Li4P2O7 and PrPO4 in the complex.

[0027] The feed rates of precursor solution A and precursor solution B are 0.5–1 mL / min, e.g., 0.5 mL / min. During the addition step in step S3, the system temperature is heated to 60–80°C, e.g., 60°C. The addition step in step S3 is carried out under ultrasonic and stirring conditions. The reaction temperature can increase the reaction rate.

[0028] According to an embodiment of the present invention, the solvent used for demulsification is ethanol. The concentration of ethanol in the demulsification system is 50 ppm, i.e., the volume ratio of ethanol to emulsion is 1:2. The separation can be centrifugation, such as centrifugation at 10,000 rpm for 10 minutes. The method further includes a step of vacuum drying at 80°C for 6 hours after collecting the powder.

[0029] According to an embodiment of the present invention, the powder is heated to 200-300°C (e.g., 300°C) at a rate of 2-5°C / min (e.g., 2°C / min) and held for 2-4 hours (e.g., 2 hours) before calcination. The core purpose of this low-temperature holding (e.g., 200-300°C for 2 hours) is to lay the foundation for subsequent high-temperature calcination through gentle treatment: it allows organic matter such as PLA-PEG and citric acid to decompose slowly, thoroughly removes residual impurities (e.g., ethanol, dichloromethane), and reduces high-temperature carbonization pollution; simultaneously, it alleviates the thermal stress difference between lithium cobalt oxide and the precursor layer, enhances interfacial bonding, and promotes Pr 3+ Li + PO4 3- The initial orderly arrangement provides a uniform template for the subsequent crystallization of Li4P2O7-PrPO4 at high temperatures, ensuring the integrity and stability of the coating layer.

[0030] The calcination temperature is 700-800℃ and the time is 5-8 hours, such as holding at 700℃ for 5 hours.

[0031] Thirdly, the present invention provides a lithium-ion battery comprising a coated and modified high-voltage lithium cobalt oxide cathode material as described in any of the preceding claims or a coated and modified high-voltage lithium cobalt oxide cathode material prepared by the method described in any of the preceding claims.

[0032] The present invention has the following beneficial effects:

[0033] (1) This invention achieves interface stabilization of high-voltage lithium cobalt oxide cathode materials at 4.7 V by constructing a Li4P2O7-PrPO4 composite coating layer. This composite coating layer combines ionic conductivity and chemical inertness, effectively suppressing electrolyte decomposition, transition metal dissolution, and lattice oxygen loss. Compared with traditional single-phase coating methods, this invention utilizes an oil-in-water emulsion system to achieve uniform deposition and tight bonding of the coating layer, resulting in controllable structure, mild process, and good repeatability. The prepared material exhibits higher capacity retention and cycle stability at high voltage, significantly improving the electrochemical performance and safety of high-energy-density lithium cobalt oxide cathodes. The cathode material of this invention achieves a capacity retention of 97.3% after 200 cycles and still retains 178.0 mAh·g at 5C.

[0034] (2) The present invention has the advantages of simple process, high controllability and suitability for large-scale production in its preparation method. Through the liquid-solid combined water-in-oil emulsion system, the in-situ deposition of the coating precursor on the surface of lithium cobalt oxide is realized, avoiding the problems of uneven coating and particle agglomeration in the traditional solid-phase mixing method. The peristaltic pump is used to precisely control the feed rate and ultrasonic dispersion, so that the thickness and composition ratio of the coating layer can be adjusted, and the interface bonding is more dense and stable. The whole process has low temperature, low energy consumption, and simple operation. The subsequent heat treatment conditions are mild, which can achieve high repeatability and industrial feasibility, and is significantly better than the existing complex or high-energy-consuming coating preparation process. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the modified lithium cobalt oxide coating of the present invention.

[0036] Figure 2 The image shows the XRD pattern of the coated modified lithium cobalt oxide prepared in Example 1 of this invention.

[0037] Figure 3 The image shows the XRD pattern of the coating layer prepared in Example 1 of this invention.

[0038] Figure 4 The cycling performance of the coated modified lithium cobalt oxide prepared in Example 1 of this invention.

[0039] Figure 5 The rate performance of the coated modified lithium cobalt oxide prepared in Example 1 of this invention. Detailed Implementation

[0040] To better understand the purpose, technical solution, and advantages of this invention, the following detailed description of a method for preparing a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material is provided in conjunction with the accompanying drawings and embodiments. However, the scope of protection of this invention is not limited to the following description.

[0041] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0042] Unless otherwise specified, the methods used in the following embodiments are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0043] Example 1

[0044] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.02, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e., 30wt% Li4P2O7 / 70wt% PrPO4).

[0045] according to Figure 1 The flowchart shown illustrates the preparation of a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material. The specific steps are as follows:

[0046] (1) Take 2g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200 W), then pass 10 mg / L ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0047] (2) Prepare template agent: Take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000, and stir until completely dissolved.

[0048] (3) Preparation of precursor solution A: Dissolve 0.0362 g praseodymium acetate and 0.00750 g lithium acetate in 30 mL of deionized water, add 0.044 g citric acid as a chelating agent, and stir until completely dissolved.

[0049] (4) Prepare precursor solution B: Dissolve 0.0262 g of ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0050] (5) The template agent is slowly added to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min. After sonication (300 W power, ice water bath to prevent overheating) and stirring at 400 rpm for 30 min, a lithium cobalt oxide water-in-oil suspension emulsion is formed.

[0051] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0052] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0053] (8) The dried powder was placed in a muffle furnace and heated to 300°C at 2°C / min for 2 hours. Then it was calcined at 700°C for 5 hours to obtain coated lithium cobalt oxide.

[0054] The coated lithium cobalt oxide obtained in Example 1 was subjected to XRD testing, and the test results are as follows: Figure 2 As shown in the figure, the coated lithium cobalt oxide retains its layered structure, exhibits no impurity peaks, and demonstrates good crystallinity. Simultaneously, the coating layer was synthesized separately, and XRD analysis was performed on it; the results are shown in the figure. Figure 3 As shown, the XRD patterns reveal the spectra of PrPO4 and Li4P2O7.

[0055] Coating layer synthesis steps: After processing the lithium cobalt oxide in step (1), filter it to separate the lithium cobalt oxide powder, leaving only the solution. Other steps remain unchanged.

[0056] Example 2

[0057] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.01, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e., 30wt% Li4P2O7 / 70wt% PrPO4).

[0058] according to Figure 1 The flowchart shown illustrates the preparation of a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material. The specific steps are as follows:

[0059] (1) Take 2 g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200W), then pass 10 mg / L ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0060] (2) Prepare template agent: Take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000, and stir until completely dissolved.

[0061] (3) Preparation of precursor solution A: Dissolve 0.0181 g praseodymium acetate and 0.00557 g lithium oxalate in 30 mL deionized water, add 0.0319 g citric acid as a chelating agent, and stir until completely dissolved.

[0062] (4) Prepare precursor solution B: Dissolve 0.0111 g of phosphoric acid in 10 mL of deionized water and stir until completely dissolved.

[0063] (5) The template agent is slowly added to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min. After sonication (300 W power, ice water bath to prevent overheating) and stirring at 400 rpm for 30 min, a lithium cobalt oxide water-in-oil suspension emulsion is formed.

[0064] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0065] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0066] (8) After drying, the powder is placed in a muffle furnace and heated to 300℃ at 2℃ / min for 2 hours. Then, it is calcined at 700℃ for 5 hours to obtain coated lithium cobalt oxide.

[0067] Example 3

[0068] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.03, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e., 30wt% Li4P2O7 / 70wt% PrPO4).

[0069] according to Figure 1 The flowchart shown illustrates the preparation of a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material. The specific steps are as follows:

[0070] (1) Take 2 g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200W), then pass 10 mg / L ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0071] (2) Preparation of template agent: Take 20 mL of dichloromethane and add 0.2 g of PLA-PEG with a molecular weight of 5000. Stir until completely dissolved.

[0072] (3) Preparation of precursor solution A: Dissolve 0.0741 g praseodymium nitrate and 0.0112 g lithium acetate in 30 mL of deionized water, add 0.0762 g citric acid as a chelating agent, and stir until completely dissolved.

[0073] (4) Prepare precursor solution B: Dissolve 0.0393 g of ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0074] (5) The template agent is slowly added to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min. After sonication (300 W power, ice water bath to prevent overheating) and stirring at 400 rpm for 30 min, a lithium cobalt oxide water-in-oil suspension emulsion is formed.

[0075] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0076] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0077] (8) After drying, the powder is placed in a muffle furnace and heated to 300℃ at 2℃ / min for 2 hours. Then, it is calcined at 700℃ for 5 hours to obtain coated lithium cobalt oxide.

[0078] Example 4

[0079] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.04, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e., 30wt% Li4P2O7 / 70wt% PrPO4).

[0080] according to Figure 1 The flowchart shown illustrates the preparation of a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material. The specific steps are as follows:

[0081] (1) Take 2 g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200W), then pass 10 mg / L ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0082] (2) Preparation of template agent: Take 20 mL of dichloromethane and add 0.2 g of PLA-PEG with a molecular weight of 5000. Stir until completely dissolved.

[0083] (3) Preparation of precursor solution A: Dissolve 0.0724 g praseodymium acetate and 0.0150 g lithium acetate in 30 mL of deionized water, add 0.08741 g citric acid as a chelating agent, and stir until completely dissolved.

[0084] (4) Prepare precursor solution B: Dissolve 0.0524 g of ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0085] (5) The template agent is slowly added to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min. After sonication (300 W power, ice water bath to prevent overheating) and stirring at 400 rpm for 30 min, a lithium cobalt oxide water-in-oil suspension emulsion is formed.

[0086] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0087] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0088] (8) After drying, the powder is placed in a muffle furnace and heated to 300℃ at 2℃ / min for 2 hours. Then, it is calcined at 700℃ for 5 hours to obtain coated lithium cobalt oxide.

[0089] Example 5

[0090] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.05, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e., 30wt% Li4P2O7 / 70wt% PrPO4).

[0091] according to Figure 1 The flowchart shown illustrates the preparation of a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material. The specific steps are as follows:

[0092] (1) Take 2 g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200W), then pass 10 mg / L ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0093] (2) Preparation of template agent: Take 20 mL of dichloromethane and add 0.2 g of PLA-PEG with a molecular weight of 5000. Stir until completely dissolved.

[0094] (3) Preparation of precursor solution A: Dissolve 0.0905 g praseodymium acetate and 0.0187 g lithium acetate in 30 mL of deionized water, add 0.1091 g citric acid as a chelating agent, and stir until completely dissolved.

[0095] (4) Prepare precursor solution B: Dissolve 0.0665 g of ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0096] (5) The template agent is slowly added to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min. After sonication (300 W power, ice water bath to prevent overheating) and stirring at 400 rpm for 30 min, a lithium cobalt oxide water-in-oil suspension emulsion is formed.

[0097] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0098] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0099] (8) The dried powder was placed in a muffle furnace and heated to 300°C at 2°C / min for 2 hours. Then it was calcined at 700°C for 5 hours to obtain coated lithium cobalt oxide.

[0100] Example 6

[0101] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.02, and the molar ratio of Li4P2O7 to PrPO4 is 1:2.5 (i.e., 25wt% Li4P2O7 / 75wt% PrPO4).

[0102] according to Figure 1 The flowchart shown illustrates the preparation of a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material. The specific steps are as follows:

[0103] (1) Take 2g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200 W), then pass 100ppm ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0104] (2) Prepare template agent: Take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000, and stir until completely dissolved.

[0105] (3) Prepare precursor solution A: Dissolve 0.040 g praseodymium acetate and 0.0130 g lithium acetate in 30 mL of deionized water, add 0.0403 g citric acid as a chelating agent, and stir until completely dissolved.

[0106] (4) Prepare precursor solution B: Dissolve 0.0260 g of ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0107] (5) Add the template agent at a constant speed of 0.5 mL / min to the lithium cobalt oxide wet suspension, sonicate (power 300 W, ice water bath to prevent overheating) and stir at 400 rpm for 30 min to form a lithium cobalt oxide water-in-oil suspension emulsion.

[0108] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0109] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0110] (8) The dried powder was placed in a muffle furnace and heated to 300°C at 2°C / min for 2 hours. Then it was calcined at 700°C for 5 hours to obtain coated lithium cobalt oxide.

[0111] Example 7

[0112] This embodiment provides a coated and modified 4.7V high-voltage lithium cobalt oxide cathode material, with a core of lithium cobalt oxide and a coating layer composed of a composite of Li4P2O7-PrPO4. The mass ratio of lithium cobalt oxide to the coating layer is 1:0.02, and the molar ratio of Li4P2O7 to PrPO4 is 1:1.5 (i.e., 35wt% Li4P2O7 / 65wt% PrPO4).

[0113] (1) Take 2g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonically clean for 10 min (power 200 W), then pass 10 mg / L ozone through the mixture under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA and continue stirring to form a suspension for later use.

[0114] (2) Prepare template agent: Take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000, and stir until completely dissolved.

[0115] (3) Prepare precursor solution A: Dissolve 0.034 g praseodymium acetate and 0.019 g lithium acetate in 30 mL of deionized water, add citric acid as a chelating agent, and stir until completely dissolved. (4) Prepare precursor solution B: Dissolve 0.0290 g ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0116] (5) The template agent is slowly added to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min. After sonication (300 W power, ice water bath to prevent overheating) and stirring at 400 rpm for 30 min, a lithium cobalt oxide water-in-oil suspension emulsion is formed.

[0117] (6) Precursor solution A and precursor solution B are slowly added to the lithium cobalt oxide water-in-oil suspension emulsion using a peristaltic pump, with the feed rate controlled at 0.5 mL / min. At the same time, the system is heated to 60°C and ultrasonically stirred.

[0118] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifuge (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6 hours.

[0119] (8) The dried powder was placed in a muffle furnace and heated to 300°C at 2°C / min for 2 hours. Then it was calcined at 700°C for 5 hours to obtain coated lithium cobalt oxide.

[0120] Comparative Example 1

[0121] Compared with Example 1, the lithium cobalt oxide coating in this comparative example does not contain Pr element, that is, praseodymium acetate is not added in step (3); the other steps are the same.

[0122] Comparative Example 2

[0123] Compared with Example 1, the lithium cobalt oxide coating in this comparative example does not contain Li element, that is, lithium acetate is not added in step (3); the other steps are the same.

[0124] Comparative Example 3

[0125] Compared with Example 1, the lithium cobalt oxide coating in this comparative example does not contain Pr element, but instead Pr element is replaced by doping modification, that is, the same amount of Pr element doped lithium cobalt oxide is used in step (1); praseodymium acetate is not added in step (3); other steps are the same.

[0126] Comparative Example 4

[0127] Compared with Example 1, this comparative example does not include praseodymium acetate and lithium acetate in step (3); the other steps are the same.

[0128] Performance test examples

[0129] Lithium cobalt oxide obtained in Examples 1-5 and Comparative Examples 1-4 was used as the positive electrode active material. A slurry was prepared by uniformly mixing the active material, conductive carbon black, and PVDF in a mass ratio of 8:1:1, and then coated onto aluminum foil as the positive electrode. A 2032-type coin cell was assembled using lithium metal sheets as the negative electrode. The electrochemical performance of the coin cells was tested at 25°C and 3.0-4.7 V. The test results are shown in Table 1. The cycle performance curve of Example 1 is shown below. Figure 4 As shown, the coated lithium cobalt oxide obtained in Example 1 has excellent cycle performance.

[0130] Meanwhile, rate performance testing was conducted on Example 1. The test conditions were 5 cycles each at 0.1 C, 0.2 C, 1 C, 2 C, 5 C, and 0.1 C. Figure 5 As shown, the coated lithium cobalt oxide exhibits excellent rate performance. This is because the fast ion conductor Li4P2O7 promotes lithium-ion transport on the surface.

[0131] Table 1. Battery material performance of each embodiment and comparative example

[0132]

[0133] As shown in the table above, Example 1 exhibits the highest capacity retention, the best electrochemical stability, and the highest discharge specific capacity at a high rate of 5 C. This indicates that the Li4P2O7-PrPO4 coating effectively suppresses the electrode interface side reactions of lithium cobalt oxide at 4.7 V, while simultaneously promoting improved rate performance.

[0134] Comparing Example 1 with Examples 2-5, it was found that the electrochemical performance was optimal when the mass ratio of lithium cobalt oxide to coating layer was 1:0.02. When the proportion of coating layer was too low (1:0.01), the coating layer could not be evenly distributed on the surface of lithium cobalt oxide and could not play a role in stabilizing the surface of lithium cobalt oxide to the greatest extent. When the proportion of coating layer was too high, it was not entirely beneficial to improve cycle stability.

[0135] Comparing Example 1 with Examples 6-7, it was found that the electrochemical performance was optimal when the molar ratio of Li4P2O7 to PrPO4 was 1:2. This is because when the proportion of PrPO4 is too high, it severely hinders the electrochemical performance of Li4P2O7. +Transport will significantly increase the internal resistance of the electrode, leading to a decrease in the initial discharge specific capacity; when the proportion of Li4P2O7 is too large, the ability to suppress oxidation side reactions and Co dissolution under high voltage is weak, resulting in a decrease in cycle stability.

[0136] Comparing Example 1 with Comparative Example 1, it can be seen that the surface PrPO4 coating layer plays a positive role in the cycling stability of lithium cobalt oxide at 4.7 V. This may be because PrPO4 helps stabilize surface lattice oxygen and inhibits the dissolution of transition metal elements, thereby enhancing the stability of the surface and interface structure.

[0137] Comparing Example 1 and Comparative Example 2, Example 1 exhibits a specific capacity of 178.0 mAh / g at a 5 C rate, significantly higher than the 158.3 mAh / g of Comparative Example 2. This is because without the addition of lithium, a Li4P2O7 phase cannot form on the surface. Li4P2O7 is a fast ion conductor, which facilitates the transport of lithium ions on the surface. It also isolates the surface from the electrolyte, reducing interfacial side reactions, thus resulting in superior rate performance.

[0138] Comparing Example 1 and Comparative Example 3, it can be seen that when Pr is used for doping modification of lithium cobalt oxide, it cannot play a positive role in the electrochemical performance of lithium cobalt oxide at a high voltage of 4.7 V. This is because at a high voltage of 4.7 V, the main reason affecting its performance is the side reaction at the surface and interface. Therefore, if Pr is used for doping modification, it has little impact on performance.

[0139] Comparing Example 1 and Comparative Example 4, it can be seen that the coated and modified lithium cobalt oxide exhibits significantly improved electrochemical performance, a markedly enhanced capacity retention, and excellent rate performance compared to the uncoated sample. This is due to the synergistic effect of Li4P2O7 and PrPO4, which stabilizes the surface lattice oxygen while reducing surface side reactions, and the fast ion conductor promotes the lithium-ion transport rate.

[0140] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A coated and modified high-voltage lithium cobalt oxide cathode material, characterized in that, It includes a core and a coating layer disposed on the surface of the core, wherein the core is lithium cobalt oxide and the coating layer includes a Li4P2O7-PrPO4 composite.

2. The coated and modified high-voltage lithium cobalt oxide cathode material according to claim 1, characterized in that: The mass ratio of the core to the coating layer is 1:(0.01~0.05).

3. The coated and modified high-voltage lithium cobalt oxide cathode material according to claim 2, characterized in that: The mass ratio of the core to the coating layer is 1:(0.02~0.05).

4. The coated and modified high-voltage lithium cobalt oxide cathode material according to claim 3, characterized in that: The mass ratio of the core to the coating layer is 1:0.

02.

5. The high-voltage lithium cobalt oxide cathode material with coating modification according to any one of claims 1-4, characterized in that: In the Li4P2O7-PrPO4 composite, the molar ratio of Li4P2O7 to PrPO4 is 1:(1.5~2.5).

6. The coated and modified high-voltage lithium cobalt oxide cathode material according to claim 5, characterized in that: In the Li4P2O7-PrPO4 composite, the molar ratio of Li4P2O7 to PrPO4 is 1:

2.

7. The method for preparing the coated and modified high-voltage lithium cobalt oxide cathode material according to any one of claims 1-6, characterized in that, Includes the following steps: S1. After mixing lithium cobalt oxide powder and water, ozone is introduced for treatment. After treatment, a surfactant is added to obtain a wet suspension of lithium cobalt oxide. S2. Add the template agent to the system obtained in step S1 for processing to obtain a lithium cobalt oxide water-in-oil suspension emulsion; S3. Precursor solution A containing praseodymium source, lithium source and chelating agent and precursor solution B containing phosphate source are respectively added to the lithium cobalt oxide oil-in-water suspension emulsion to obtain the emulsion system. S4. Add solvent to the emulsion system to break the emulsion and separate and collect the powder. S5. The powder is calcined to obtain the coated and modified high-voltage lithium cobalt oxide cathode material.

8. The preparation method according to claim 7, characterized in that: Before introducing ozone in step S1, the mixture of lithium cobalt oxide powder and water is subjected to ultrasonic treatment. The concentration of ozone in the mixture of lithium cobalt oxide powder and water is (5-10) mg / L; The ozone treatment time is 10–30 min; The surfactant is EDTA, and the mass ratio of lithium cobalt oxide to the surfactant is 1:(0.02~0.05).

9. The preparation method according to claim 7 or 8, characterized in that: The template agent is PLA-PEG; The template agent is added in the form of an organic solution of PLA-PEG, with dichloromethane as the solvent, wherein the mass of PLA-PEG in each 20 mL of dichloromethane is 0.1–0.2 g; The feed rate of the template agent in the system obtained in step S1 is 0.5 to 1 mL / min.

10. The preparation method according to any one of claims 7-9, characterized in that: The praseodymium source is selected from any one of praseodymium acetate, praseodymium nitrate, and praseodymium chloride; The lithium source is selected from any one of lithium acetate, lithium oxalate, and lithium nitrate. The chelating agent is citric acid; The molar ratio of the chelating agent to the metal ions in the praseodymium source and the lithium source is 1:1; The phosphoric acid source is selected from one or more of ammonium dihydrogen phosphate and phosphoric acid; The feed rates of precursor solution A and precursor solution B are 0.5 to 1 mL / min, respectively; While adding the product as described in step S3, the system is heated to 60-80°C.

11. The preparation method according to any one of claims 7-10, characterized in that: The solvent used for demulsification is ethanol; The concentration of ethanol in the demulsification system is 50 ppm; The powder is heated to 200-300℃ at a rate of 2-5℃ / min and held for 2-4 hours before calcination; The calcination temperature is 700–800 °C, and the time is 5–8 h.

12. A lithium-ion battery, characterized in that, The high-voltage lithium cobalt oxide cathode material with coating modification according to any one of claims 1-6 or the high-voltage lithium cobalt oxide cathode material with coating modification prepared by the method according to any one of claims 7-11 is included.

13. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 12.

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