Coated modified high-voltage lithium cobalt oxide positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention discloses a coated modified high-voltage lithium cobalt oxide positive electrode material, a preparation method thereof and a lithium ion battery. The coated and modified high-voltage lithium cobalt oxide positive electrode material comprises an inner core and a coating layer arranged on the surface of the inner core, the inner core is lithium cobalt oxide, and the coating layer comprises a Li4P2O7-PrPO4 compound. According to the invention, the Li4P2O7-PrPO4 composite coating layer is constructed on the surface of the lithium cobalt oxide, so that the interface stabilization of the high-voltage lithium cobalt oxide positive electrode material under the condition of 4.7 V is realized. The composite coating layer has ionic conductivity and chemical inertness, and can effectively inhibit electrolyte decomposition, transition metal dissolution and lattice oxygen loss. The prepared material shows higher capacity retention ratio and cycling stability under high voltage, and the electrochemical performance and safety of a high-energy-density lithium cobalt oxide positive electrode are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a coated modified high-voltage lithium cobaltate cathode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Under the urgent needs of global energy transformation and sustainable development, lithium ion batteries have become the core energy storage technology in the fields of portable electronic devices, electric vehicles, large-scale energy storage systems, etc. due to their high energy density, long cycle life, low self-discharge rate and environmental friendliness. With the continuous improvement of battery performance requirements in related application scenarios, it has become a key target and core challenge in the field of research and development to continuously optimize the comprehensive performance of lithium ion batteries, especially the energy density and cycle stability.

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

[0004] Among them, lithium cobaltate (LiCoO2) is the earliest layered cathode material to achieve large-scale commercialization. Due to its high theoretical capacity (~274 mAh / g), high compaction density, stable electrochemical performance, etc., it has long dominated the high-end consumer electronics market. However, conventional lithium cobaltate (working voltage usually ≤4.45 V vs. Li ＋ / Li) is prone to crystal structure instability (such as irreversible phase transition), accelerated surface and interface side reactions (such as electrolyte decomposition, transition metal ion dissolution), etc. in the deep delithiation state (high state of charge SOC), which limits its actual reversible capacity (usually only about 140-155 mAh / g) and significantly reduces its cycle stability. These problems severely restrict the full performance of lithium cobaltate materials.

[0005] To fully tap the energy density potential of lithium cobalt oxide, raising the charge cut-off voltage to above 4.5 V (such as 4.6 V, 4.7 V or even higher) is an important technical path. Existing modification methods and their limitations: To address the stability problems of lithium cobalt oxide (including high-voltage types), existing technologies mainly use two strategies of element doping and surface coating. By introducing hetero-metal ions (such as Al, Mg, Ti, La, etc.) into the lattice, the aim is to stabilize the crystal structure, suppress phase transition and reduce oxygen loss. However, the doping effect is limited by the element type, concentration and distribution uniformity, and the improvement effect on the severe surface interface problem at high voltage is limited; coating modification is to build a physical / chemical barrier on the surface of lithium cobalt oxide particles, which is the most direct and effective means to isolate the positive active material from the electrolyte and suppress the interface side reaction. The coating layer can significantly improve the interface stability of the material at high voltage, reduce electrolyte decomposition and transition metal dissolution, but there are still some bottleneck problems to be solved in traditional coating technology. Especially under extreme conditions of 4.7 V or even higher voltage, more stringent requirements are put forward for the composition design, microstructure control (such as thickness, coverage, porosity) and preparation process of the coating layer Therefore, developing a new preparation method that can build an ultra-thin, uniform, dense, strong and tough coating layer with excellent compatibility with high-voltage lithium cobalt oxide matrix has important scientific significance and engineering application value for fully tapping the potential of 4.7 V high-voltage lithium cobalt oxide, achieving synergistic improvement of high energy density and long cycle life. SUMMARY

[0006] The purpose of the present application is to provide a coated modified high-voltage lithium cobalt oxide positive electrode material, its preparation method and lithium ion battery, by building a Li4P2O7-PrPO4 composite coating layer on the surface of the lithium cobalt oxide positive electrode material, improving the surface structure stability of the lithium cobalt oxide, improving the near-surface lithium ion transport rate, thereby improving the rate performance and cycle stability of the lithium cobalt oxide, to improve the electrochemical performance at 4.7 V cut-off voltage.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows: In a first aspect, the present application provides a coated modified high-voltage lithium cobalt oxide positive electrode material, comprising a core and a coating layer arranged on the surface of the core, the core is lithium cobalt oxide, and the coating layer comprises a Li4P2O7-PrPO4 composite.

[0008] Based on the above technical scheme, in order to solve the problems of serious surface side reaction and decline of surface and interface stability of the lithium cobalt oxide in the cycle process under high voltage, a composite coating layer containing PrPO4 and Li4P2O7 is constructed, which can not only stabilize the surface crystal structure by PrPO4 to construct a stable CEI layer, but also improve the rate performance of the lithium cobalt oxide by the fast ion conductor composed of Li4P2O7. The inventors find that, compared with doping in the lithium cobalt oxide, the coating modification of the positive electrode material by applying Pr element in the surface coating layer has better electrochemical performance.

[0009] According to an embodiment of the application, 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 find that, when the mass ratio of the core to the coating layer is too low, it cannot play a role in stabilizing the surface of the lithium cobalt oxide to the maximum extent, and when the ratio of the coating layer is too high, it is not completely beneficial to the improvement of the cycle stability.

[0010] According to an embodiment of the application, 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, 1:2.5. In a preferred embodiment of the application, the molar ratio (Li4P2O7:PrPO4) in the Li4P2O7-PrPO4 composite is approximately 1:2, i.e. about 30 wt% Li4P2O7 / 70 wt% PrPO4. Among them, about 70 wt% PrPO4 can form a continuous and dense protective layer to inhibit oxidation / side reaction; about 30 wt% Li4P2O7 is sufficient to form ion conduction channels or local Li dissolution points in the protective layer to avoid the negative effects of "complete isolation". If the proportion of PrPO4 phase is too large, although PrPO4 is chemically stable, the electronic / ionic conductivity is poor, and too thick will significantly increase the internal resistance of the electrode, resulting in capacity loss or rate reduction. If the proportion of Li4P2O7 phase is too large, although it is beneficial to Li ion transmission, it has weak inhibition ability to oxidation side reaction and Co dissolution under high voltage, resulting in decline of cycle stability.

[0011] In a second aspect, the application provides a preparation method of the coating-modified high-voltage lithium cobalt oxide positive electrode material described in any one of the above, comprising the following steps: S1, mixing lithium cobalt oxide powder and water, then introducing ozone for treatment, adding a surfactant after the treatment is completed to obtain a lithium cobalt oxide wet suspension; S2, adding a template agent to the system obtained in step S1 for treatment to obtain a lithium cobalt oxide oil-in-water suspension emulsion; S3, precursor solution A containing a praseodymium source, a lithium source and a chelating agent and precursor solution B containing a phosphoric acid source are added into the lithium cobalt oxide oil-in-water suspension emulsion respectively to obtain an emulsion system; S4, a solvent is added to the emulsion system to perform demulsification, and a powder is collected and separated; S5, the powder is calcined to obtain the coated modified high-voltage lithium cobalt oxide positive electrode material.

[0012] Based on the above technical scheme, the emulsion template method is adopted to construct a Li4P2O7-PrPO4 composite coating layer on the surface of the lithium cobalt oxide positive electrode material, and the electrochemical performance of the lithium cobalt oxide at a high voltage of 4.7 V is effectively improved. The principle of synthesizing the Li4P2O7-PrPO4 coated lithium cobalt oxide by the emulsion template method is as follows: first, the surface of the lithium cobalt oxide is activated by ozone to generate active groups, then a template is added to the water phase suspension thereof, ultrasonic stirring is performed to form an oil-in-water emulsion of the lithium cobalt oxide, and PLA-PEG is used to stabilize the interface and construct a reaction space. Subsequently, a chelating precursor containing Pr 3+ , Li + and PO4 3- is slowly added, and is directionally deposited on the surface of the lithium cobalt oxide under the limited action; after demulsification by ethanol and drying to remove organic matter, two-step calcination is performed to decompose the precursor and cause a solid-phase reaction, and finally a dense composite coating layer is formed, and the emulsion template effectively avoids random precipitation of the precursor, and ensures the uniformity of the coating.

[0013] According to the embodiment of the present application, the ratio of the lithium cobalt oxide powder and water is (1-5) g: 50 mL, including but not limited to 2 g: 50 mL.

[0014] In step S1, before the ozone is introduced, the mixed system of the lithium cobalt oxide powder and water is subjected to ultrasonic treatment, for example, ultrasonic treatment at 200 W for 10 min. The ultrasonic treatment can clean the lithium cobalt oxide powder.

[0015] The concentration of the ozone in the mixed system of the lithium cobalt oxide powder and water is 5-10 mg / L, for example, 10 mg / L. The time for which the ozone is introduced for treatment is 10-30 min. The ozone is decomposed in water to generate hydroxyl radicals, which can slightly oxidize the surface of the lithium cobalt oxide, increase the density of the surface hydroxyl groups, and be beneficial to the adsorption of the oxygen-containing anion (phosphate) and the subsequent precipitation reaction.

[0016] The surfactant is EDTA, and the mass ratio of the lithium cobalt oxide to the surfactant is 1: (0.02-0.05), for example, 1:0.05. The surfactant can reduce the liquid-solid interfacial tension, make the precursor solution more easily wet the surface of the lithium cobalt oxide, and promote the uniform nucleation of the coating layer.

[0017] According to an embodiment of the present application, the template agent is PLA-PEG. The template agent is added in the form of an organic solution of PLA-PEG, the solvent being dichloromethane, wherein the mass of PLA-PEG is 0.1-0.2 g per 20 mL of dichloromethane, including but not limited to 0.2 g. As an example, the molecular weight of PLA-PEG is 5000. The feeding speed 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 the conditions of ultrasonic and stirring, such as ultrasonic at 300 W and stirring at 400 rpm for 30 min.

[0018] According to an embodiment of the present application, the praseodymium source is selected from any one of praseodymium acetate, praseodymium nitrate, praseodymium chloride. The lithium source is selected from any one of lithium acetate, lithium oxalate, lithium nitrate. The molar ratio of the praseodymium source to the lithium source is (0.375-0.625):1, including but not limited to 0.375:1, 0.5:1, 0.625:1, in particular 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 phase precipitation and force the precipitation reaction to occur only on the surface of lithium cobaltate, thereby forming a dense, uniform and firmly bonded nanoscale coating layer.

[0019] The phosphoric acid source is selected from one or more of ammonium dihydrogen phosphate, phosphoric acid. The molar ratio of the phosphoric acid source to the praseodymium source is (1.8-2.3):1, including but not limited to 2.3:1, 2:1, 1.8:1, in particular can be adjusted according to the molar ratio of Li4P2O7 and PrPO4 in the composite.

[0020] The feeding speed of the precursor solution A and the precursor solution B is 0.5-1 mL / min, such as 0.5 mL / min, respectively. The system temperature is heated to 60-80°C, such as 60°C, at the same time as the adding step in step S3. The adding step in step S3 is carried out under the conditions of ultrasonic and stirring. The reaction temperature can increase the reaction rate.

[0021] According to an embodiment of the present application, the solvent for demulsification is ethanol. The concentration of the ethanol in the demulsification system is 50 ppm, i.e. the volume ratio of ethanol to emulsion is 1:2. The separation can be centrifugal separation, such as centrifugation at 10000 rpm for 10 min. The method further comprises a step of vacuum drying at 80°C for 6 h after collecting the powder.

[0022] According to an embodiment of the present application, the powder is raised to 200-300°C (e.g. 300°C) at a rate of 2-5°C / min (e.g. 2°C / min) and kept for 2-4h (e.g. 2h) before calcination. The core purpose of the low-temperature keeping (e.g. 200-300°C, keeping for 2h) is to lay a foundation for subsequent high-temperature calcination through mild treatment: it can not only allow the slow decomposition of PLA-PEG, citric acid and other organic matters, but also completely remove residual impurities (e.g. ethanol, dichloromethane) to reduce high-temperature carbonization pollution; at the same time, it can relieve the thermal stress difference between lithium cobalt oxide and the precursor layer, enhance the interface bonding force, and promote the preliminary ordered arrangement of Li4P2O7-PrPO4 to provide a uniform template for the crystallization of Li4P2O7-PrPO4 at a subsequent high temperature, thereby ensuring the integrity of the coating layer and the stability of the performance. 3+ + 3- The preliminary ordered arrangement provides a uniform template for the crystallization of Li4P2O7-PrPO4 at a subsequent high temperature, thereby ensuring the integrity of the coating layer and the stability of the performance.

[0023] The calcination temperature is 700-800°C, and the time is 5-8h, e.g. keeping at 700°C for 5h.

[0024] In a third aspect, the present application provides a lithium ion battery comprising the coating-modified high-voltage lithium cobalt oxide cathode material of any one of the above or the coating-modified high-voltage lithium cobalt oxide cathode material prepared by the method of any one of the above.

[0025] The present application has the following advantages: (1) The present application realizes the interface stabilization of high-voltage lithium cobalt oxide cathode material under the condition of 4.7 V by constructing a Li4P2O7-PrPO4 composite coating layer. The composite coating layer has ion conductivity and chemical inertness, which can effectively inhibit the decomposition of electrolyte, the dissolution of transition metal and the loss of lattice oxygen. Compared with the traditional single-phase coating method, the present application uses the oil-in-water emulsion system to realize the uniform deposition and close combination of the coating layer, and has controllable structure, mild process and good repeatability. The prepared material has higher capacity retention rate and cycle stability at high voltage, which significantly improves the electrochemical performance and safety of high-energy-density lithium cobalt oxide cathode. The capacity retention rate of the cathode material of the present application after 200 cycles reaches 97.3%, and it still has 178.0 mAh.g at 5C.

[0026] (2) The present application has the advantages of simple process, high controllability and suitability for large-scale production in the preparation method. Through the liquid-solid combined oil-in-water emulsion system, the in-situ deposition of the coating precursor on the surface of lithium cobalt oxide is realized, which avoids the problems of uneven coating, particle agglomeration and the like in the traditional solid-phase mixing method. The use of peristaltic pump to accurately control the feeding rate and ultrasonic dispersion makes the thickness and composition ratio of the coating layer adjustable, and the interface combination more dense and stable. The whole process has low temperature, small energy consumption and simple operation, and the subsequent heat treatment conditions are mild, which can realize high repeatability and industrial feasibility, and is significantly superior to the existing complex or high-energy-consumption coating preparation process.​​ Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the modified lithium cobalt oxide coating of the present invention.

[0028] Figure 2 The image shows the XRD pattern of the coated modified lithium cobalt oxide prepared in Example 1 of this invention.

[0029] Figure 3 The image shows the XRD pattern of the coating layer prepared in Example 1 of this invention.

[0030] Figure 4 The cycling performance of the coated modified lithium cobalt oxide prepared in Example 1 of this invention.

[0031] Figure 5 The rate performance of the coated modified lithium cobalt oxide prepared in Example 1 of this invention. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Example 1 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).

[0036] 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: (1) Take 2 g of bare lithium cobaltate powder, add 50 mL of deionized water, ultrasonic cleaning for 10 min (power 200 W), then pass 10 mg / L ozone under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA, continue stirring to make a suspension for standby.

[0037] (2) Template agent: take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000, stir until completely dissolved.

[0038] (3) Configure precursor solution A: take 0.0362 g of praseodymium acetate and 0.00750 g of lithium acetate, dissolve in 30 mL of deionized water, add 0.044 g of citric acid as a chelating agent, stir until completely dissolved.

[0039] (4) Configure precursor solution B: take 0.0262 g of ammonium dihydrogen phosphate, dissolve in 10 mL of deionized water, stir until completely dissolved.

[0040] (5) Slowly add the template agent to the lithium cobaltate wet suspension at a specific flow rate of 0.5 mL / min, ultrasonic (power 300 W, ice water bath to prevent overheating) and stir at 400 rpm for 30 min to form a lithium cobaltate oil-in-water suspension emulsion.

[0041] (6) Slowly add precursor solution A and precursor solution B to the lithium cobaltate oil-in-water suspension emulsion through a peristaltic pump, control the feeding speed to be 0.5 mL / min, and at the same time heat the system to 60℃, keep ultrasonic stirring.

[0042] (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℃ for 6h.

[0043] (8) Place the dried powder in a muffle furnace, first increase the temperature to 300℃ at a rate of 2 ℃ / min, keep the temperature for 2h, then calcine at 700℃ for 5h to obtain coated lithium cobaltate.

[0044] The coated lithium cobaltate obtained in Example 1 was subjected to XRD test, and the test results are shown in Figure 2 . The coated lithium cobaltate still maintains a layered structure, no impurity peak, good crystallinity. At the same time, the coating layer was synthesized alone and subjected to XRD test, and the test results are shown in Figure 3 . The XRD spectrum shows the spectrum of PrPO4 and Li4P2O7.

[0045] Coating layer synthesis steps: filter the lithium cobaltate after step (1), separate the lithium cobaltate powder, and only leave the solution. Other steps remain unchanged.

[0046] Example 2 The present example provides a coated modified 4.7V high-voltage lithium cobalt oxide cathode material, the core is lithium cobalt oxide, the coating layer is 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).

[0047] The coated modified 4.7V high-voltage lithium cobalt oxide cathode material is prepared according to the flowchart shown in the figure, and the specific steps are as follows: Figure 1 (1) Take 2 g of bare lithium cobalt oxide powder, add 50 mL of deionized water, ultrasonic cleaning for 10 min (power 200 W), then pass 10 mg / L ozone under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA, continue to stir to form a suspension for standby.

[0048] (2) Prepare the 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.

[0049] (3) Prepare precursor solution A: take 0.0181 g of praseodymium acetate and 0.00557 g of lithium oxalate, dissolve in 30 mL of deionized water, add 0.0319 g of citric acid as a chelating agent, and stir until completely dissolved.

[0050] (4) Prepare precursor solution B: take 0.0111 g of phosphoric acid and dissolve in 10 mL of deionized water, and stir until completely dissolved.

[0051] (5) Slowly add the template agent to the lithium cobalt oxide wet suspension at a specific flow rate of 0.5 mL / min, ultrasonic (power 300 W, ice water bath to prevent overheating) and 400 rpm stirring for 30 min to form a lithium cobalt oxide oil-in-water suspension emulsion.

[0052] (6) Slowly add precursor solution A and precursor solution B to the lithium cobalt oxide oil-in-water suspension emulsion through a peristaltic pump, control the feeding speed to be 0.5 mL / min, and at the same time heat the system to 60°C, keep ultrasonic stirring.

[0053] (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 6h.

[0054] ​(8) The dried powder is placed in a muffle furnace, first increased to 300°C at 2°C / min, and then calcined at 700°C for 5h to obtain the coated lithium cobaltate.

[0055] Example 3 The present example provides a coated modified 4.7V high-voltage lithium cobaltate cathode material, the core is lithium cobaltate, the coating layer is a composite of Li4P2O7-PrPO4, the mass ratio of lithium cobaltate to coating layer is 1:0.03, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e. 30wt% Li4P2O7 / 70wt% PrPO4).

[0056] The coated modified 4.7V high-voltage lithium cobaltate cathode material is prepared according to the flowchart shown in Figure 1 The specific steps are as follows: (1) Take 2 g of bare lithium cobaltate powder, add 50 mL of deionized water, ultrasonic cleaning for 10 min (power 200 W), then pass 10 mg / L ozone under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA, continue stirring to form a suspension for standby.

[0057] (2) Prepare the template agent: take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000. Stir until completely dissolved.

[0058] (3) Prepare precursor solution A: take 0.0741 g of praseodymium nitrate, 0.0112 g of lithium acetate, and 0.0762 g of citric acid as a chelating agent, and dissolve them in 30 mL of deionized water. Stir until completely dissolved.

[0059] (4) Prepare precursor solution B: take 0.0393 g of ammonium dihydrogen phosphate and dissolve it in 10 mL of deionized water. Stir until completely dissolved.

[0060] (5) Slowly add the template agent to the lithium cobaltate wet suspension at a specific flow rate of 0.5 mL / min, ultrasonic (power 300 W, ice water bath to prevent overheating) and 400 rpm stirring for 30 min to form a lithium cobaltate oil-in-water suspension emulsion.

[0061] (6) Slowly add precursor solution A and precursor solution B to the lithium cobaltate oil-in-water suspension emulsion through a peristaltic pump, control the feeding speed to be 0.5 mL / min, and at the same time heat the system to 60°C, keep ultrasonic stirring.

[0062] (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 6h.

[0063] (8) After drying, the powder is placed in a muffle furnace, first increased to 300°C at 2°C / min, kept for 2h, then calcined at 700°C for 5h to obtain the coated lithium cobaltate.

[0064] Example 4 This example provides a coated modified 4.7V high-voltage lithium cobaltate cathode material, the core is lithium cobaltate, the coating layer is a composite of Li4P2O7-PrPO4, the mass ratio of lithium cobaltate to coating layer is 1:0.04, and the molar ratio of Li4P2O7 to PrPO4 is 1:2 (i.e. 30wt% Li4P2O7 / 70wt% PrPO4).

[0065] The coated modified 4.7V high-voltage lithium cobaltate cathode material is prepared according to the flowchart shown in Figure 1 The specific steps are as follows: (1) Take 2 g of bare lithium cobaltate powder, add 50 mL of deionized water, ultrasonic clean for 10 min (power 200 W), then pass 10 mg / L ozone under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA, continue to stir to form a suspension for standby.

[0066] (2) Prepare the template agent: take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000. Stir until completely dissolved.

[0067] (3) Prepare precursor solution A: take 0.0724 g of praseodymium acetate, 0.0150 g of lithium acetate, and 0.08741 g of citric acid as a chelating agent, and dissolve them in 30 mL of deionized water. Stir until completely dissolved.

[0068] (4) Prepare precursor solution B: take 0.0524 g of ammonium dihydrogen phosphate and dissolve it in 10 mL of deionized water. Stir until completely dissolved.

[0069] (5) Slowly add the template agent to the lithium cobaltate wet suspension at a specific flow rate of 0.5 mL / min, ultrasonic (power 300 W, ice water bath to prevent overheating) and stir at 400 rpm for 30 min to form a lithium cobaltate oil-in-water suspension emulsion.

[0070] (6) Slowly add precursor solution A and precursor solution B to the lithium cobaltate oil-in-water suspension emulsion through a peristaltic pump, control the feeding speed to be 0.5 mL / min, and at the same time heat the system to 60°C, keep ultrasonic stirring.

[0071] (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.

[0072] (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.

[0073] Example 5 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).

[0074] 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: (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.

[0075] (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.

[0076] (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.

[0077] (4) Prepare precursor solution B: Dissolve 0.0665 g of ammonium dihydrogen phosphate in 10 mL of deionized water and stir until completely dissolved.

[0078] (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.

[0079] (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.

[0080] (7) To the emulsion system obtained in step (5), 50 mL of ethanol was added to break the emulsion, and the powder was collected by centrifugation (10000 rpm, 10 min) and placed in a vacuum drying oven at 80°C for 6h.

[0081] (8) The dried powder was placed in a muffle furnace, first increased to 300°C at a rate of 2°C / min, and then kept at this temperature for 2h. After calcination at 700°C for 5h, the coated lithium cobalt oxide was obtained.

[0082] Example 6 This example provides a coated modified 4.7V high-voltage lithium cobalt oxide cathode material, with lithium cobalt oxide as the core and a composite of Li4P2O7-PrPO4 as the coating layer. 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).

[0083] The coated modified 4.7V high-voltage lithium cobalt oxide cathode material was prepared according to the flowchart shown in FIG. 1, and the specific steps are as follows: Figure 1 (1) Take 2g of bare lithium cobalt oxide powder, add 50 mL of deionized water, and ultrasonically clean for 10 min (power 200 W). Then, under stirring at 400 rpm, 100 ppm of ozone was introduced for 30 min, followed by the addition of 0.1 g of EDTA, and the mixture was stirred to form a suspension for later use.

[0084] (2) Template preparation: Take 20 mL of dichloromethane, add 0.2 g of PLA-PEG with a molecular weight of 5000, and stir until completely dissolved.

[0085] (3) Preparation of precursor solution A: Take 0.040 g of praseodymium acetate and 0.0130 g of lithium acetate, dissolve them in 30 mL of deionized water, and add 0.0403 g of citric acid as a chelating agent. Stir until completely dissolved.

[0086] (4) Preparation of precursor solution B: Take 0.0260 g of ammonium dihydrogen phosphate, dissolve it in 10 mL of deionized water, and stir until completely dissolved.

[0087] (5) Slowly add the template at a constant speed of 0.5 mL / min to the lithium cobalt oxide wet suspension, and ultrasonically (power 300 W, ice water bath to prevent overheating) and stir at 400 rpm for 30 min to form a lithium cobalt oxide oil-in-water suspension emulsion.

[0088] ​(6) Slowly add precursor solution A and precursor solution B into the lithium cobaltate oil-in-water suspension emulsion through a peristaltic pump, control the feeding speed to be 0.5 mL / min, and at the same time, heat the system to 60°C, and keep ultrasonic stirring.

[0089] (7) Add 50 mL of ethanol to the emulsion system obtained in step (5) to break the emulsion, centrifugal separation (10000 rpm, 10 minutes) to collect the powder and place it in a vacuum drying oven at 80°C for 6h.

[0090] (8) Place the dried powder in a muffle furnace, first increase the temperature to 300°C at a rate of 2°C / min, keep the temperature for 2h, then calcine at 700°C for 5h, to obtain the coated lithium cobaltate.

[0091] Example 7 The present example provides a coated modified 4.7V high-voltage lithium cobaltate cathode material, the core is lithium cobaltate, the coating layer is a composite of Li4P2O7-PrPO4, the mass ratio of lithium cobaltate to coating layer is 1:0.02, and the molar ratio of Li4P2O7 to PrPO4 is 1:1.5 (i.e. 35wt% Li4P2O7 / 65wt% PrPO4).

[0092] (1) Take 2g of bare lithium cobaltate powder, add 50 mL of deionized water, ultrasonic cleaning for 10 min (power 200 W), then pass 10 mg / L ozone under stirring at 400 rpm for 30 min, then add 0.1 g of EDTA, continue stirring to form a suspension for standby.

[0093] (2) Prepare the 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.

[0094] (3) Prepare precursor solution A: take 0.034 g of praseodymium acetate and 0.019 g of lithium acetate, dissolve in 30 mL of deionized water, add citric acid as a chelating agent, and stir until completely dissolved. (4) Prepare precursor solution B: take 0.0290 g of ammonium dihydrogen phosphate, dissolve in 10 mL of deionized water, and stir until completely dissolved.

[0095] (5) Slowly add the template agent to the lithium cobaltate wet suspension at a specific flow rate of 0.5 mL / min, ultrasonic (power 300 W, ice water bath to prevent overheating) and stir at 400 rpm for 30 min to form a lithium cobaltate oil-in-water suspension emulsion.

[0096] (6) Precursor solution A and precursor solution B were slowly added into the lithium cobaltate oil-in-water suspension emulsion by peristaltic pump, the feeding speed was controlled at 0.5 mL / min, and the system was heated to 60°C at the same time, and ultrasonic stirring was maintained.

[0097] (7) 50 mL of ethanol was added to the emulsion system obtained in step (5) to break the emulsion, and the powder was collected by centrifugation (10000 rpm, 10 minutes) and placed in a vacuum drying oven at 80°C for 6h.

[0098] (8) The dried powder was placed in a muffle furnace, first increased to 300°C at a rate of 2 ℃ / min, and then kept at 700°C for 5h to obtain the coated lithium cobaltate.

[0099] Comparative Example 1 This comparative example is compared with Example 1, the lithium cobaltate coating layer does not contain Pr element, i.e. no praseodymium acetate is added in step (3); other steps are the same. Comparative Example 2 This comparative example is compared with Example 1, the lithium cobaltate coating layer does not contain Li element, i.e. no lithium acetate is added in step (3); other steps are the same.

[0100] Comparative Example 3 This comparative example is compared with Example 1, the lithium cobaltate coating layer does not contain Pr element, but the Pr element is modified by doping, i.e. the same content of Pr element doped lithium cobaltate is used in step (1); no praseodymium acetate is added in step (3); other steps are the same.

[0101] Comparative Example 4 This comparative example is compared with Example 1, no praseodymium acetate and lithium acetate is added in step (3); other steps are the same.

[0102] Performance Test Example The lithium cobaltate obtained in Examples 1-5 and Comparative Examples 1-4 was used as the positive electrode material active substance, and a slurry was prepared by uniformly mixing the active substance, conductive carbon black and PVDF in a mass ratio of 8:1:1, and then coated on an aluminum foil as a positive electrode, and a metal lithium sheet was used as a negative electrode to assemble a 2032 type button cell. The button cell was subjected to electrochemical performance test under the conditions of 25°C and 3.0-4.7 V, and the test results are shown in Table 1. The cycle performance curve of Example 1 is shown in Figure 4 The coated lithium cobaltate obtained in Example 1 has excellent cycle performance.

[0103] At the same time, the rate performance test of Example 1 was carried out, the test conditions were 0.1 C, 0.2 C, 1 C, 2 C, 5 C, and 0.1 C, each cycle for 5 times, as shown in Figure 5The coated lithium cobaltate has excellent rate performance. This is because the fast ion conductor Li4P2O7 promotes the transmission of lithium ions on the surface.

[0104] Table 1, battery material performance of each example and comparative example

[0105] As can be seen from the above table, the capacity retention of Example 1 is the highest, the electrochemical stability is the best, and the discharge specific capacity at 5 C high rate is the highest. It shows that the coating layer composed of Li4P2O7-PrPO4 effectively inhibits the electrode interface side reaction of lithium cobaltate at 4.7 V, and at the same time promotes the improvement of rate performance.

[0106] Comparing Example 1 with Examples 2-5, it is found that when the mass ratio of lithium cobaltate to coating layer is 1:0.02, the electrochemical performance is the best, when the ratio of the coating layer is too low (1:0.01), the coating layer cannot be evenly distributed on the surface of lithium cobaltate, and cannot play the role of stabilizing the surface of lithium cobaltate to the maximum extent, and when the ratio of the coating layer is too high, it is not completely beneficial to the improvement of cycle stability.

[0107] Comparing Example 1 with Examples 6-7, it is found that when the molar ratio of Li4P2O7 and PrPO4 is 1:2, the electrochemical performance is the best, because when the proportion of PrPO4 phase is too large, it seriously hinders the Li + transportation, which will significantly increase the internal resistance of the electrode, resulting in a decrease in the initial discharge specific capacity; when the proportion of Li4P2O7 phase is too large, the inhibition ability to oxidation side reaction and Co dissolution at high voltage is weak, resulting in a decrease in cycle stability.

[0108] Comparing Example 1 with Comparative Example 1, it is found that the surface PrPO4 coating layer plays a positive role in the cycle stability of lithium cobaltate at 4.7 V, which may be due to the fact that PrPO4 is beneficial to the stability of the surface lattice oxygen, and at the same time inhibits the dissolution of transition metal elements, so that the stability of the surface interface structure is enhanced.

[0109] Comparing Example 1 with Comparative Example 2, it is found that Example 1 has a specific capacity of 178.0 mAh / g at 5 C rate, which is much larger than 158.3 mAh / g of Comparative Example 2. This is because no lithium element is added, and the surface cannot form Li4P2O7 phase. Li4P2O7 is a fast ion conductor, which is beneficial to the transmission of lithium ions on the surface, and at the same time has the effect of isolating the surface from the electrolyte and reducing the interface side reaction, so the rate performance is excellent.

[0110] From Comparative Example 1 and Comparative Example 3, it can be seen that when Pr element is used for doping modification of lithium cobaltate, it cannot play a positive role in the electrochemical performance of lithium cobaltate at a high voltage of 4.7 V, because the main reason affecting the performance at a high voltage of 4.7 V is the side reaction of the surface interface, and therefore the effect of Pr on the performance is small if it is used for doping modification.

[0111] From Comparative Example 1 and Comparative Example 4, it can be seen that the electrochemical performance of the coated modified lithium cobaltate is obviously improved compared with the uncoated sample, the capacity retention rate is significantly improved, and the rate performance is excellent. This is because the synergistic effect of Li4P2O7 and PrPO4 stabilizes the surface lattice oxygen while reducing the surface side reaction, and the fast ion conductor promotes the transmission rate of lithium ions.

[0112] The above describes the present application in detail. For those skilled in the art, the present application can be implemented in a wider range under equivalent parameters, concentrations and conditions without departing from the purpose and scope of the present application. Although the present application gives a special example, it should be understood that the present application can be further improved. In summary, according to the principle of the present application, the present application intends to include any change, use or improvement of the present application, including changes made by conventional techniques known in the art, which deviates from the range disclosed in the present application.

Claims

1. A coated modified high-voltage lithium cobalt oxide cathode material, characterized in that, The core is lithium cobalt oxide, and the coating layer comprises a Li4P2O7-PrPO4 composite.

2. The coating-modified high-voltage lithium cobalt oxide cathode material of claim 1, characterized by: The mass ratio of the core to the coating layer is 1:(0.01-0.05), preferably 1:(0.02-0.05), and more preferably 1:0.

02.

3. The coating-modified high-voltage lithium cobalt oxide cathode material according to claim 1 or 2, characterized in that: In the Li4P2O7-PrPO4 composite, the molar ratio of Li4P2O7 to PrPO4 is 1:(1.5-2.5), preferably 1:

2.

4. The method of producing the coating-modified high-voltage lithium cobalt oxide cathode material according to any one of claims 1 to 3, characterized in that The method comprises the following steps: S1, mixing lithium cobalt oxide powder and water, then introducing ozone for treatment, adding a surfactant after the treatment, and obtaining a lithium cobalt oxide wet suspension; S2, adding a template agent to the system obtained in step S1 for treatment, and obtaining a lithium cobalt oxide oil-in-water suspension emulsion; S3, adding a precursor solution A comprising a praseodymium source, a lithium source and a chelating agent, and a precursor solution B comprising a phosphoric acid source to the lithium cobalt oxide oil-in-water suspension emulsion respectively, and obtaining an emulsion system; S4, adding a solvent to the emulsion system for demulsification, and collecting the powder; S5, calcining the powder to obtain the coating-modified high-voltage lithium cobalt oxide positive electrode material.

5. The method of claim 4, wherein: In step S1, before the ozone is introduced, the mixed system of lithium cobalt oxide powder and water is subjected to ultrasonic treatment; The concentration of the ozone in the mixed system 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 the lithium cobalt oxide to the surfactant is 1:(0.02-0.05).

6. The production method according to claim 4 or 5, characterized in that: The template agent is PLA-PEG; The template agent is added in the form of an organic solution of PLA-PEG, and the solvent is dichloromethane, wherein the mass of PLA-PEG in 20 mL of dichloromethane is 0.1-0.2 g; The feeding speed of the template agent in the system obtained in step S1 is 0.5-1 mL / min.

7. The method of any one of claims 4-6, wherein: 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 feeding speeds of the precursor solution A and the precursor solution B are 0.5-1 mL / min respectively; In step S3, the system is heated to 60-80°C at the same time as the steps are added.

8. The method of any one of claims 4-7, wherein: The demulsification solvent is ethanol; The concentration of the ethanol in the demulsification system is 50 ppm; Before calcination, the powder is raised to 200-300°C at a rate of 2-5°C / min and kept for 2-4 h; The calcination temperature is 700-800°C, and the time is 5-8 h.

9. A lithium-ion battery, characterized by The coating-modified high-voltage lithium cobalt oxide positive electrode material of any one of claims 1-3 or prepared by the method of any one of claims 4-8.

10. An electrical device, characterized by The lithium ion battery of claim 9.

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