Preparation method of lithium-rich layered positive electrode material

Abstract

The invention discloses a preparation method of a lithium-rich layered positive electrode material, and belongs to the technical field of battery materials. According to the preparation method, through the unique steps of precursor preparation, microwave reaction, high-temperature sintering, three-step surface modification and the like, the stability of oxygen is effectively improved, and oxygen release is reduced. The hierarchical pore structure, the oxygen vacancies and the surface nanosheets cooperate with one another and act together. The hierarchical pore structure provides a rapid lithium ion diffusion channel, oxygen vacancies ensure oxygen stability and electronic conductivity, and the surface nanosheets protect the material and increase the specific surface area. The synergistic mechanism enables the lithium-rich layered positive electrode material to be remarkably improved in the aspects of specific capacity, cycling stability, rate capability, thermal stability and the like, and can better meet the requirements of the next generation of lithium ion batteries on the positive electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a method for preparing a lithium-rich layered positive electrode material. Background Art

[0002] At present, the commercialized cathode materials for lithium-ion batteries mainly include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4) and lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, NCM), lithium nickel cobalt aluminum oxide (LiNi 1-x- y Co x Al y O2, NCA) ternary oxide cathode materials (Zhang Jia, Zhu Zehua, Wang Haifeng, Research status of lithium-manganese-rich layered cathode materials for lithium-ion batteries [J]. Power Supply Technology, 2015, 39(6): 1323-1326). The specific energy of single cells prepared with these commercialized cathode materials is less than 200W·h / kg, which cannot meet the needs of further improving the specific energy of lithium-ion batteries.

[0003] Lithium-rich layered oxides (LLOs) cathode materials have cation and anion redox reactions, which give them ultra-high specific capacity and make them one of the highly anticipated cathode material candidates for next-generation lithium-ion batteries. However, the anion redox reaction of LLOs cathode materials is also considered a "double-edged sword". While providing additional capacity, this reaction also causes LLOs cathode materials to have problems such as oxygen release and poor cycle stability, which seriously restrict their practical application. Irreversible redox reactions not only trigger reactions with the electrolyte, leading to the release of large amounts of Joule heat, but also destroy the lattice structure of LLOs cathode materials, thereby adversely affecting battery safety. Therefore, reducing the large amount of oxygen released is a key factor in improving the thermal stability of LLOs cathode materials, and the key to alleviating oxygen release from LLOs cathode materials lies in improving oxygen stability.

[0004] In a large number of current studies, strategies such as cation doping and surface coating are widely used to improve the structural stability of LLOs cathode materials. Among them, cation doping can not only form stronger M-O bonds by occupying transition metal sites with cations, thereby enhancing the stability of oxygen, but also partially cation doping can increase the interlayer spacing of the crystal plane, thereby improving the diffusion rate of lithium ions.

[0005] For example, Chinese patent application CN202310472877.X discloses a high-entropy lithium-rich layered positive electrode material for marine environment and a preparation method thereof, belonging to the technical field of battery energy materials. The chemical formula of the positive electrode material is: Li1+nMnxNiyCozTMaO2, wherein TM is one or more of Na, Mg, Zn, Al, Fe, Ti and Mo, n=0.2, x=0.16 or 0.52, 0.12≤y≤0.16, 0.12≤z≤0.16, a=0.04 or 0.32, and n+x+y+z+a=1. The patent combines sanding and high-temperature sintering process to prepare high-entropy lithium-rich positive electrode material. The material has a 0.1C discharge specific capacity of more than 300 mAh / g, and a 1C rate capacity retention rate of more than 90% after 100 cycles. By adjusting the proportion and type of doped elements, high-entropy lithium-rich positive electrode materials with different performances can be obtained.

[0006] However, the cation doping of this patent only stays on the surface of the material and does not really penetrate into the bulk structure of the material, so it does not inhibit oxygen release from the root, and the battery thermal stability cannot meet the actual use requirements.

[0007] Therefore, how to optimize the microstructure of the positive electrode material, inhibit oxygen release, and improve the electrochemical performance of the material is a technical problem to be solved for the current lithium-rich layered positive electrode material. SUMMARY

[0008] The present application provides a preparation method of a lithium-rich layered positive electrode material to optimize the microstructure of the positive electrode material, inhibit oxygen release, and improve the electrochemical performance of the material. The preparation method effectively improves the stability of oxygen, reduces oxygen release, and improves the electrochemical performance of the material through unique precursor preparation, microwave reaction, high-temperature sintering, and three-step surface modification.

[0009] To achieve the above technical purpose, the technical solution adopted by the present application is: A preparation method of a lithium-rich layered positive electrode material, the positive electrode material is prepared by a co-precipitation method to prepare a precursor, and then obtained by three-step surface modification, the specific steps are: (1) Precursor preparation: first, prepare a 2.0 mol / L metal salt solution by mixing nickel salt, cobalt salt and manganese salt, and prepare a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia solution at the same time, then gradually add the three solutions to a continuously heated and stirred reaction kettle at the same time, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80℃, the reaction is aged for 40-48h, and the suspension emulsion A is obtained after completion; (2) Microwave reaction: the suspension emulsion A is transferred into a high-pressure closed microwave reactor, and then microwave heating is performed at 190-200℃ and 2-3MPa for 2-4 hours. After cooling to room temperature, the high-pressure reactor is opened, and the reaction product is centrifuged, washed with water and ethanol alternately for three times, and dried in a vacuum drying oven at 100-110℃ for 10-15 hours to obtain the precursor material B; (3) High-temperature sintering: the precursor material B and lithium salt are mixed and ground uniformly at a molar ratio of 1.2:1, and the powder is heated at a rate of 5℃ / min in a muffle furnace, sintered at 400℃ for 4h, and then sintered at 800℃ for 8h to obtain the original lithium-rich manganese-based material C; (4) Surface modification 1: NaBH4 is dissolved in deionized water to prepare a 2-3mol / L solution, and the lithium-rich manganese-based material C is added to the solution. After continuous stirring for 15-30min, it is filtered and placed in a vacuum drying oven for 12h. The dried powder is sintered at 350℃ for 3h in an argon atmosphere containing 5-10% H2 to obtain the lithium-rich manganese-based material D; (5) Surface modification 2: 0.1 mol / L ethyl silicate TEOS is dissolved in anhydrous ethanol, and 0.05 mol / L dilute ammonia water is added to adjust the pH of the system to 9.5-10. The mixture is stirred at 40℃ for 30min to form a transparent SiO2 sol. The lithium-rich manganese-based material D obtained by surface modification 1 is dispersed in the above sol, and ultrasonic treatment is performed for 20-30min. The mixture is continuously stirred at 55-60℃ for 3-4h; (6) Surface modification 3: the mixture is transferred to a hydrothermal kettle, and urea and cetyltrimethylammonium bromide CTAB are added. The temperature is increased to 180℃ at a rate of 2℃ / min, and the temperature is maintained for 6h to promote the directional growth of SiO2 on the material surface into nanosheets, and the temperature is naturally lowered; (7) Post-processing: after centrifugation, the product is washed with ethanol for 3 times, vacuum dried at 75-80℃ for 12-15h, and then sintered at 350-400℃ for 2h in a N2 atmosphere to obtain the final product, the lithium-rich layered positive electrode material.

[0010] Further, the nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0011] Further, the volume ratio of the metal salt solution, the Na2CO3 solution and the ammonia water in step (1) is 1:1:0.5.

[0012] Further, the lithium salt in step (3) is one or more of lithium hydroxide, lithium nitrate or lithium carbonate.

[0013] Further, the mass ratio of NaBH4 powder to the lithium-rich manganese-based material C in step (4) is 2:1.

[0014] Further, the solid-liquid ratio of the lithium-rich manganese-based material D and the sol in step (5) is 1:50 g / mL, and the volume ratio of ethyl silicate and anhydrous ethanol is 1:8.

[0015] Further, the mass ratio of the lithium-rich manganese-based material D, urea and cetyltrimethylammonium bromide CTAB in step (6) is 1:0.3-0.5:0.4.

[0016] Beneficial effects: The present application significantly improves the structural stability and electrochemical performance of the lithium-rich layered positive electrode material through the triple synergistic mechanism of multi-level pore structure design, oxygen vacancy regulation and surface nanosheet construction: 1. Multi-level pore structure design: In the preparation process, the steps of precursor preparation and microwave reaction help to form a multi-level pore structure. This micro-nano porous structure provides more diffusion channels for lithium ions, shortens the diffusion path of lithium ions, and thus improves the diffusion rate of lithium ions. In the charging and discharging process, lithium ions can be more quickly embedded and extracted from the positive electrode material, improving the charging and discharging efficiency and rate performance of the battery.

[0017] 2. Oxygen vacancy regulation: In the surface modification step, especially using NaBH4 solution to treat the lithium-rich manganese-based material C, appropriate oxygen vacancies can be introduced. The presence of oxygen vacancies can enhance the stability of oxygen and reduce oxygen release. In the battery charging and discharging process, a stable oxygen environment can inhibit irreversible redox reactions, reduce the degree of reaction with electrolyte, reduce the release of Joule heat, and improve the thermal stability and safety performance of the battery. At the same time, oxygen vacancies can also adjust the electronic structure of the material, which is beneficial to improve the electronic conductivity of the material and further improve the electrochemical performance.

[0018] 3. Surface nanosheet construction: Through surface modification 2 and surface modification 3, SiO2 nanosheets are grown on the surface of the material. These nanosheets can act as a protective layer to prevent direct contact between the electrolyte and the positive electrode material, reducing the erosion and dissolution of the positive electrode material by the electrolyte, thereby improving the cycle stability of the material. In addition, the presence of nanosheets can also increase the specific surface area of the material, increase the contact area between the material and the electrolyte, and be beneficial to the transmission and exchange of lithium ions, further improving the performance of the battery.

[0019] 4. Synergistic effect: the three of hierarchical porous structure, oxygen vacancies and surface nanosheets synergize with each other. The hierarchical porous structure provides fast lithium ion diffusion channels, the oxygen vacancies ensure the stability of oxygen and electronic conductivity, and the surface nanosheets protect the material and increase the specific surface area. This synergistic mechanism makes the lithium-rich layered cathode material have significant improvement in specific capacity, cycle stability and thermal stability, and can better meet the requirements of the next generation of lithium-ion batteries for cathode materials. After testing, the lithium-rich layered cathode material prepared by the preparation method of the present application has a specific capacity of more than 300 mAh / g at a charge-discharge rate of 0.1C, and the capacity retention rate can still reach more than 90% after 200 cycles at a rate of 1C, showing excellent electrochemical performance. In practical application, the material can provide higher specific energy for lithium-ion batteries to meet the market demand for high-energy-density batteries, and is expected to promote the wider application of lithium-ion batteries in electric vehicles, portable electronic devices and other fields. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Scanning electron microscope images of the precursor B prepared for Example 1 of the present application at different magnifications; Figure 2 Scanning electron microscope images of the lithium-rich layered cathode material prepared for Example 1 of the present application; Figure 3 Charge-discharge curve of the lithium-rich layered cathode material prepared for Example 1 of the present application at a rate of 0.1C; Figure 4 Cycle performance spectrum of the lithium-rich layered cathode material prepared for Example 1 of the present application at a rate of 1C; Figure 5 Cycle performance spectrum of the cathode material prepared for Comparative Examples 1-5 of the present application at a rate of 1C; Figure 6 DSC test results of the lithium-rich layered cathode material prepared for Example 1 of the present application; Figure 7 Scanning electron microscope images of the cathode material prepared for Comparative Examples 3-4. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be further described below in conjunction with specific embodiments, but are not limited thereto.

[0022] Example 1 A preparation method of a lithium-rich layered cathode material, the cathode material is prepared by a co-precipitation method to prepare a precursor, and then obtained by three-step surface modification, the specific steps are as follows: (1) Precursor preparation: first, the nickel salt, cobalt salt and manganese salt are prepared into a 2.0 mol / L metal salt solution, and a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia solution are prepared at the same time, then the three solutions are gradually added into a continuously heated and stirred reaction kettle at the same time, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80°C, the reaction is aged for 40h, and the suspension emulsion A is obtained after completion; (2) Microwave reaction: the suspension emulsion A is transferred into a high-pressure sealed reaction kettle for microwave heating, and then microwave hydrothermal reaction is carried out at 190-200°C and a pressure of 2-3 MPa for 2 hours, cooled to room temperature, the high-pressure reaction kettle is opened, the reaction product is centrifuged, washed with water and ethanol alternately three times, and dried in a vacuum drying oven at 100-110°C for 10 hours to obtain the precursor material B; the microwave hydrothermal reaction (190-200°C, 2-3 MPa) can promote the rearrangement of the precursor lattice through molecular-level instantaneous heating, form submicron particles with few defects and high crystallinity, and form a uniform porous structure. On the one hand, it provides an ideal substrate for subsequent surface treatment, on the other hand, such a structure can provide more active sites for contact with electrolyte during charging and discharging, which is beneficial to the rapid embedding and extraction of lithium ions, thereby improving the specific capacity of the material; at the same time, such a structure is beneficial to the diffusion of lithium ions in the material, shortens the diffusion path of lithium ions, reduces the diffusion resistance, and further improves the charge-discharge rate performance of the material. The precursor structure is as follows Figure 1 .

[0023] (3) High-temperature sintering: the precursor material B and lithium salt are mixed and ground uniformly according to a molar ratio of 1.2:1, the powder is heated at a rate of 5°C / min in a muffle furnace, first sintered at 400°C for 4h, then sintered at 800°C for 8h, to obtain the original lithium-rich manganese-based material C; (4) Surface modification 1: NaBH4 is dissolved in deionized water and stirred to prepare a 2 mol / L solution, the lithium-rich manganese-based material C is added to the solution, and continuously stirred for 15 min, then filtered and placed in a vacuum drying oven for 12h, and the dried powder is sintered at 350°C for 3h in an argon gas mixture containing 5-10% H2 to obtain the lithium-rich manganese-based material D; NaBH4 sintering (350°C) in a H2 / Ar atmosphere can induce the material to form oxygen vacancies and partially reduced transition metals, enhancing the Mn-O bond energy. Compared with traditional doping (only surface modification), oxygen vacancies fundamentally improve oxygen stability, reducing the cycle capacity decay rate. Oxygen vacancies and subsequent SiO2 nanosheet coating form a complement, the former inhibits the loss of bulk oxygen, and the latter blocks the surface erosion of electrolyte, together delaying the irreversible transformation of the layered structure to spinel / rock salt phase.

[0024] (5) Surface modification 2: 0.1 mol / L ethyl silicate TEOS is dissolved in anhydrous ethanol, 0.05 mol / L dilute ammonia water is added, the pH of the system is adjusted to 9.5-10, and the hydrolysis is stirred at 40°C for 30 min to form a transparent SiO2sol; the lithium-rich manganese-based material D obtained in surface modification 1 is dispersed in the sol, and ultrasonic treatment is performed for 20 min, and continuous stirring is performed at 55-60°C for 3 h; (6) Surface modification 3: the mixture is transferred to a hydrothermal kettle, urea and cetyltrimethylammonium bromide CTAB are added, the temperature is increased to 180°C at a rate of 2°C / min, and the temperature is kept for 6 h; CTAB acts as a structure-directing agent to form a micellar template by self-assembly, guiding the directional growth of SiO2nanosheets on the surface of the material; urea hydrolysis provides a uniform alkaline environment to promote TEOS hydrolysis and condensation; surface modifications 2-3 grow SiO2nanosheets on the surface of the material by sol-gel and hydrothermal methods to form a uniform coating layer. Such a nanosheet coating layer reduces electrolyte contact, SiO2enhances Li + diffusion, relieves the stress of cyclic phase change, and further improves the electrochemical performance. At the same time, the SiO2coating layer and oxygen vacancies synergistically inhibit the release of lattice oxygen, reduce gas evolution during charging and discharging, and improve thermal stability.

[0025] (7) Post-processing: after centrifugal separation, washing with ethanol 3 times, vacuum drying at 75-80°C for 12 h, and then sintering at 350-400°C for 2 h under N2atmosphere to obtain the final product lithium-rich layered cathode material (the morphology is shown in Figure 2

[0026] The nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0027] The volume ratio of the metal salt solution, the Na2CO3 solution, and the ammonia water in step (1) is 1:1:0.5.

[0028] The lithium salt in step (3) is lithium hydroxide.

[0029] The mass ratio of NaBH4 powder to lithium-rich manganese-based material C in step (4) is 2:1.

[0030] The solid-liquid ratio of lithium-rich manganese-based material D and sol in step (5) is 1:50 g / mL, and the volume ratio of ethyl silicate and anhydrous ethanol is 1:8.

[0031] The mass ratio of lithium-rich manganese-based material D, urea, and cetyltrimethylammonium bromide CTAB in step (6) is 1:0.3:0.4.

[0032] Example 2 ​A preparation method of a lithium-rich layered positive electrode material, the positive electrode material being prepared by a co-precipitation method to prepare a precursor, and then being obtained after three-step surface modification, the specific steps being: (1) Precursor preparation: first, prepare a 2.0 mol / L metal salt solution by mixing nickel salt, cobalt salt and manganese salt, and then prepare a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia water solution, then, add the three solutions into a continuously heated and stirred reaction kettle at the same time, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80°C, and the reaction is aged for 48 hours, and then a suspension emulsion A is obtained; (2) Microwave reaction: transfer the suspension emulsion A into a high-pressure sealed microwave reaction kettle, then perform microwave heating, and microwave hydrothermal reaction is performed at 190-200°C and a pressure of 2-3 MPa for 4 hours, then cool to room temperature, open the high-pressure reaction kettle, centrifuge the reaction product, wash with water and ethanol alternately for three times, and then dry in a vacuum drying oven at 100-110°C for 15 hours to obtain a precursor material B; (3) High-temperature sintering: mix and grind the precursor material B and lithium salt according to a molar ratio of 1.2:1, and then heat the powder in a muffle furnace at a heating rate of 5°C / min, first sinter at 400°C for 4 hours, and then sinter at 800°C for 8 hours to obtain an original lithium-rich manganese-based material C; (4) Surface modification 1: dissolve NaBH4 in deionized water to prepare a 2-3 mol / L solution, add the lithium-rich manganese-based material C into the solution, continuously stir for 30 minutes, then filter and place in a vacuum drying oven for 12 hours, and then sinter the dried powder at 350°C in an argon mixed atmosphere containing 5-10% H2 for 3 hours to obtain a lithium-rich manganese-based material D; (5) Surface modification 2: dissolve 0.1 mol / L ethyl silicate TEOS in anhydrous ethanol, add 0.05 mol / L dilute ammonia water, adjust the pH of the system to 9.5-10, and then hydrolyze at 40°C for 30 minutes to form a transparent SiO2 sol; disperse the lithium-rich manganese-based material D obtained in the surface modification 1 into the above sol, and then ultrasonic treat for 20-30 minutes and continuously stir at 55-60°C for 4 hours; (6) Surface modification 3: transfer the mixture into a hydrothermal kettle, add urea and cetyltrimethylammonium bromide CTAB, heat to 180°C at a heating rate of 2°C / min, and then keep the temperature for 6 hours to promote the directional growth of SiO2 on the material surface into nanosheets, and then naturally cool down; (7) Post-treatment: centrifuge, wash with ethanol for three times, vacuum dry at 75-80°C for 15 hours, and then sinter at 350-400°C for 2 hours in a N2 atmosphere to obtain a final product of a lithium-rich layered positive electrode material.

[0033] The nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0034] The volume ratio of the metal salt solution, the Na2CO3 solution, and the ammonia water in step (1) is 1:1:0.5.

[0035] The lithium salt in step (3) is lithium carbonate.

[0036] The mass ratio of the NaBH4 powder to the lithium-rich manganese-based material C in step (4) is 2:1.

[0037] The solid-liquid ratio of the lithium-rich manganese-based material D and the sol in step (5) is 1:50 g / mL, and the volume ratio of the ethyl silicate and the anhydrous ethanol is 1:8.

[0038] The mass ratio of the lithium-rich manganese-based material D, the urea, and the cetyltrimethylammonium bromide CTAB in step (6) is 1:0.5:0.4.

[0039] Comparative Example 1 In this comparative example, the raw materials and process steps are the same as those in Example 1, except that the microwave reaction is not performed.

[0040] A preparation method of a lithium-rich layered positive electrode material, the positive electrode material being prepared by a co-precipitation method to obtain a precursor, and then being obtained through three-step surface modification, the specific steps being: (1) Precursor preparation: first, a 2.0 mol / L metal salt solution is prepared by mixing nickel salt, cobalt salt, and manganese salt, and a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia water are prepared at the same time, then the three solutions are simultaneously and gradually added to a continuously heated and stirred reaction kettle, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80℃, the reaction is aged for 40 h, and after completion, a suspension emulsion A is obtained; (2) Centrifugal separation: the suspension emulsion A is centrifugally separated, washed with water and ethanol alternately three times, and dried in a vacuum drying oven at 100-110℃ for 10 hours to obtain a precursor material B; (3) High-temperature sintering: the precursor material B and the lithium salt are mixed and ground uniformly according to a molar ratio of 1.2:1, the powder is heated at a rate of 5℃ / min in a muffle furnace, sintered at 400℃ for 4 h, and then sintered at 800℃ for 8 h to obtain an original lithium-rich manganese-based material C; (4) Surface modification 1: NaBH4 was dissolved in deionized water to prepare a 2 mol / L solution, and the lithium-rich manganese-based material C was added to the solution. After stirring for 15 min, the mixture was filtered and placed in a vacuum drying oven for 12 h. The dried powder was sintered at 350°C for 3 h under an argon atmosphere containing 5-10% H2 to obtain a lithium-rich manganese-based material D; (5) Surface modification 2: 0.1 mol / L ethyl silicate (TEOS) was dissolved in anhydrous ethanol, and 0.05 mol / L dilute ammonia water was added to adjust the pH to 9.5-10. The mixture was stirred at 40°C for 30 min to form a transparent SiO2 sol. The lithium-rich manganese-based material D obtained by surface modification 1 was dispersed in the sol, and ultrasonic treatment was performed for 20 min. The mixture was continuously stirred at 55-60°C for 3 h; (6) Surface modification 3: The mixture was transferred to a hydrothermal kettle, and urea and cetyltrimethylammonium bromide (CTAB) were added. The temperature was increased to 180°C at a rate of 2°C / min, and the mixture was kept at this temperature for 6 h to promote the directional growth of SiO2 nanosheets on the surface of the material. The mixture was allowed to cool naturally. (7) Post-processing: After centrifugal separation, the mixture was washed with ethanol three times, dried at 75-80°C for 12 h in a vacuum drying oven, and then sintered at 350-400°C for 2 h under a N2 atmosphere to obtain the final product, a lithium-rich layered cathode material.

[0041] Comparative Example 2 In this comparative example, the raw materials and process steps were the same as in Example 1, except that surface modification 1 was not performed.

[0042] A method for preparing a lithium-rich layered cathode material, which is prepared by a co-precipitation method to obtain a precursor, and then obtained by two-step surface modification. The specific steps are as follows: (1) Preparation of precursor: First, prepare a 2.0 mol / L metal salt solution by dissolving nickel salt, cobalt salt and manganese salt. At the same time, prepare a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia solution. Then, add the three solutions to a continuously heated and stirred reaction kettle at a pH of 9-11 and a stirring speed of 300-800 rpm. The reaction temperature is 50-80°C, and the reaction is aged for 40 h. After completion, a suspension emulsion A is obtained. (2) Microwave reaction: Transfer the suspension emulsion A into a high-pressure sealed microwave reaction kettle, and then perform microwave heating at 190-200°C and a pressure of 2-3 MPa for 2 hours. Cool to room temperature, open the high-pressure reaction kettle, and centrifugally separate the reaction product. Wash with water and ethanol three times, and dry in a vacuum drying oven at 100-110°C for 10 hours to obtain a precursor material B. (3) High-temperature sintering: the precursor material B and lithium salt are mixed and ground uniformly according to a molar ratio of 1.2:1, the powder is heated in a muffle furnace at a heating rate of 5℃ / min, first sintered at 400℃ for 4h, then sintered at 800℃ for 8h, to obtain the original lithium-rich manganese-based material C; (4) Surface modification 2: 0.1 mol / L ethyl silicate TEOS is dissolved in anhydrous ethanol, 0.05 mol / L dilute ammonia water is added, the system pH is adjusted to 9.5-10, and the hydrolysis is carried out at 40℃ for 30 min to form a transparent SiO2 sol; the lithium-rich manganese-based material C obtained in step (3) is dispersed in the above sol, ultrasonic treatment is carried out for 20 min, and continuous stirring is carried out at 55-60℃ for 3 h; (5) Surface modification 3: the mixture is transferred to a hydrothermal kettle, urea and cetyltrimethylammonium bromide CTAB are added, the temperature is raised to 180℃ at a rate of 2℃ / min, and the temperature is kept for 6 h to promote the directional growth of SiO2 on the material surface into nanosheets, and the temperature is naturally lowered; (6) Post-processing: after centrifugal separation, ethanol is used for washing 3 times, vacuum drying is carried out at 75-80℃ for 12 h, and then sintering is carried out at 350-400℃ for 2 h under N2 atmosphere to obtain the final product lithium-rich layered cathode material.

[0043] The nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0044] The volume ratio of the metal salt solution, the Na2CO3 solution and the ammonia water in step (1) is 1:1:0.5.

[0045] The lithium salt in step (3) is lithium hydroxide.

[0046] The solid-liquid ratio of the lithium-rich manganese-based material C and the sol in step (4) is 1:50 g / mL, and the volume ratio of ethyl silicate and anhydrous ethanol is 1:8.

[0047] The mass ratio of the lithium-rich manganese-based material D, urea and cetyltrimethylammonium bromide CTAB in step (5) is 1:0.3:0.4.

[0048] Comparative Example 3 In this comparative example, the raw materials and process steps are the same as those in Example 1, except that the surface modification 2 treatment is not performed.

[0049] A preparation method of a lithium-rich layered cathode material, the cathode material is prepared by a co-precipitation method to obtain a precursor, and then obtained by two-step surface modification, the specific steps are as follows: (1) Precursor preparation: first, the nickel salt, cobalt salt and manganese salt are prepared into a 2.0 mol / L metal salt solution, and a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia solution are prepared, then the three solutions are simultaneously added into a continuously heated and stirred reaction kettle, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80℃, the reaction is aged for 40h, and the suspension emulsion A is obtained after completion; (2) Microwave reaction: the suspension emulsion A is transferred into a high-pressure sealed microwave reaction kettle, then microwave heating is carried out at 190-200℃, 2-3 MPa pressure for 2 hours, cooled to room temperature, the high-pressure reaction kettle is opened, the reaction product is centrifuged, washed with water and ethanol alternately for three times, and dried in a vacuum drying oven at 100-110℃ for 10 hours to obtain the precursor material B; (3) High-temperature sintering: the precursor material B and lithium salt are mixed and ground uniformly according to a molar ratio of 1.2:1, the powder is heated in a muffle furnace at a heating rate of 5℃ / min, first sintered at 400℃ for 4h, then sintered at 800℃ for 8h to obtain the original lithium-rich manganese-based material C; (4) Surface modification 1: NaBH4 is dissolved in deionized water to prepare a 2 mol / L solution, the lithium-rich manganese-based material C is added to the solution, and stirred for 15 min, then filtered and placed in a vacuum drying oven for 12h, and the dried powder is sintered at 350℃ for 3h in an argon mixed atmosphere containing 5-10% H2 to obtain the lithium-rich manganese-based material D; (5) Surface modification 3: the lithium-rich manganese-based material D is transferred to a hydrothermal kettle, and urea and cetyltrimethylammonium bromide CTAB are added and ground to mix uniformly, heated to 180℃ at a heating rate of 2℃ / min, and kept for 6h, and naturally cooled; (6) Post-processing: after centrifugation, washed with ethanol for 3 times, vacuum dried at 75-80℃ for 12h, and then sintered at 350-400℃ for 2h in N2 atmosphere to obtain the final product lithium-rich layered cathode material.

[0050] The nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0051] The volume ratio of the metal salt solution, the Na2CO3 solution and the ammonia water in step (1) is 1:1:0.5.

[0052] The lithium salt in step (3) is lithium hydroxide.

[0053] The mass ratio of NaBH4 powder to lithium-rich manganese-based material C in step (4) is 2:1.

[0054] Step (5) the mass ratio of lithium-rich manganese-based material D, urea and cetyltrimethylammonium bromide CTAB is 1:0.3:0.4.

[0055] Comparative Example 4 In this comparative example, the raw materials and process steps are the same as those in Example 1, except that the surface modification 3 is not performed.

[0056] A preparation method of a lithium-rich layered positive electrode material, the positive electrode material is prepared by a co-precipitation method to prepare a precursor, and then obtained by three-step surface modification, the specific steps are: (1) Preparation of precursor: first, prepare a 2.0 mol / L metal salt solution by mixing nickel salt, cobalt salt and manganese salt, at the same time, prepare a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia water, then, add the three solutions into a continuously heated and stirred reaction kettle at the same time, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80℃, the reaction is aged for 40 h, and then a suspension emulsion A is obtained; (2) Microwave reaction: transfer the suspension emulsion A into a high-pressure sealed microwave reaction kettle, then perform microwave heating, and microwave hydrothermal reaction at 190-200℃ and a pressure of 2-3 MPa for 2 hours, cool to room temperature, open the high-pressure reaction kettle, centrifuge the reaction product, wash with water and ethanol alternately for three times, and dry in a vacuum drying oven at 100-110℃ for 10 hours to obtain a precursor material B; (3) High-temperature sintering: mix and grind the precursor material B and lithium salt according to a molar ratio of 1.2:1, heat the powder in a muffle furnace at a heating rate of 5℃ / min, first sinter at 400℃ for 4 h, and then sinter at 800℃ for 8 h to obtain an original lithium-rich manganese-based material C; (4) Surface modification 1: dissolve NaBH4 in deionized water to prepare a 2 mol / L solution, add the lithium-rich manganese-based material C into the solution, continuously stir for 15 min, then filter and place in a vacuum drying oven for 12 h, and sinter the dried powder at 350℃ for 3 h in an argon mixed atmosphere containing 5-10% H2 to obtain a lithium-rich manganese-based material D; (5) Surface modification 2: dissolve 0.1 mol / L ethyl silicate TEOS in anhydrous ethanol, add 0.05 mol / L dilute ammonia water, adjust the pH of the system to 9.5-10, and hydrolyze at 40℃ for 30 min to form a transparent SiO2 sol; disperse the lithium-rich manganese-based material D obtained by surface modification 1 in the above sol, and ultrasonic treat for 20 min, and continuously stir at 55-60℃ for 3 h; (6) Post-treatment: After centrifugal separation, washed with ethanol for 3 times, vacuum dried at 75-80℃ for 12h, then sintered at 350-400℃ for 2h under N2 atmosphere to obtain the final product of lithium-rich layered cathode material.

[0057] The nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0058] The volume ratio of the metal salt solution, the Na2CO3 solution, and the ammonia water in step (1) is 1:1:0.5.

[0059] The lithium salt in step (3) is lithium hydroxide.

[0060] The mass ratio of NaBH4 powder to lithium-rich manganese-based material C in step (4) is 2:1.

[0061] The solid-liquid ratio of lithium-rich manganese-based material D and sol in step (5) is 1:50 g / mL, and the volume ratio of ethyl silicate to anhydrous ethanol is 1:8.

[0062] Comparative Example 5 In this comparative example, a lithium-rich layered cathode material was prepared by using the prior art.

[0063] A method for preparing a lithium-rich layered cathode material, the specific steps are: (1) Preparation of precursor: first, prepare a 2.0 mol / L metal salt solution by mixing nickel salt, cobalt salt, and manganese salt, and prepare a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia water at the same time, then gradually add the three solutions to a continuously heated and stirred reaction kettle, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80℃, and the reaction is aged for 40h, and then a suspension emulsion A is obtained; (2) Centrifugal separation: centrifugal separation of the suspension emulsion A, washing with water and ethanol alternately for three times, drying in a vacuum drying oven at 100-110℃ for 10 hours to obtain a precursor material B; (3) High-temperature sintering: mix and grind the precursor material B and lithium salt according to a molar ratio of 1.2:1, heat the powder in a muffle furnace at a heating rate of 5℃ / min, first sinter at 400℃ for 4h, and then sinter at 800℃ for 8h to obtain an original lithium-rich manganese-based material C.

[0064] The nickel salt in step (1) is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:75.

[0065] Step (1) the volume ratio of metal salt solution, Na2CO3 solution and ammonia water is 1:1:0.5.

[0066] Step (3) the lithium salt is lithium hydroxide.

[0067] Performance test The electrode materials of the examples and the comparative examples of the application were tested, and the electrode materials and battery preparation methods were as follows: The electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) were weighed according to a mass ratio of 7:2:1, put into a marver mortar, ground for 30 min to mix them uniformly, then an appropriate amount of N-methyl pyrrolidone (NMP) was added, and they were ground again for 30 min. After being mixed sufficiently, the mixed slurry was uniformly coated on an aluminum foil using a doctor blade with a thickness of 150 um, and finally dried in a vacuum drying oven at 60 ℃ for 12 h to evaporate the solvent. After drying, the electrode material was cut into a sheet with a diameter of 12 mm. The aluminum foil was also cut into a sheet with a diameter of 12 mm, and the mass of the active material of the electrode sheet was calculated after weighing. The mass of the active material of the electrode sheet was 2-2.6 mg.

[0068] The battery shell used in this experiment was CR2032 type, the lithium-rich manganese-based material was used as the positive electrode, the lithium sheet with a diameter of 14 mm was used as the negative electrode, and polyethylene was used as the separator. The half-cell assembly was carried out in a glove box under an argon atmosphere (both water and oxygen values were <0.01 ppm), LiPF6 with a concentration of 1 mol was used as the solute, and a mixture of ethyl carbonate and dimethyl carbonate (volume ratio 1:1) was used as the solvent as the electrolyte. Attention should be paid to the sequence of assembly. The electrolyte was dropped on both sides of the separator, and attention should be paid to the process of assembly to make the positive and negative electrodes as close to the middle position of the battery shell as possible. Finally, the battery was packaged using a battery sealing machine. The assembled battery was left to stand for 12 h to allow the electrolyte to fully soak, and finally the performance test was carried out on an electrochemical instrument. Each experimental group was repeated with 5 samples, and the performance test results were averaged.

[0069] Charge-discharge test: The charge-discharge test of the button cell was carried out on a battery test system (CT2001A) generated by Wuhan Blue Electronic Technology Co., Ltd. 1C was defined as 200 mAh / g, and the test voltage range was 2.0-4.8 V. After the assembled button cell was left to stand for 12 h, it was first charged and discharged at a small current of 0.1C for 3 times, and then different rates, cycle stability and other electrochemical properties were tested.

[0070] Cyclic voltammetry (CV) test: the subsequent test of the cycle performance was carried out at 1C and 2.0-4.8 V.

[0071] The morphology of the material was observed by scanning electron microscopy. The thermal stability of the material (4.8 V charged state sample) was evaluated by differential scanning calorimetry.

[0072] Table 1 Electrochemical performance From the data in Table 1, we can see that the initial specific capacity of Example 1 and Example 2 is significantly higher than that of each comparative example, which indicates that after the complete preparation of the precursor, microwave reaction, high-temperature sintering, and three-step surface modification processes, the electrochemical activity of the material has been significantly improved, and more electricity can be released during the first charge and discharge process. In terms of the first coulombic efficiency, Example 1 and Example 2 also show a high level, which means that the energy loss of the material during the first charge and discharge process is small, and the charge and discharge reversibility is better.

[0073] In terms of cycle performance, the capacity retention rates of Example 1 and Example 2 after 100 cycles and 200 cycles under 1C conditions are much higher than those of each comparative example. This fully demonstrates that the three-step surface modification process plays a key role in improving the structural stability of the material. During the charge and discharge cycle, a stable structure can effectively inhibit the structural changes of the material and the side reactions between the electrode and the electrolyte, thereby reducing the loss of active substances and ensuring the continuous output of battery capacity.

[0074] Comparative Examples 1-4 lack some key steps, resulting in different degrees of decline in their electrochemical performance. Comparative Example 1 does not perform microwave reaction, the lattice rearrangement of the precursor is not sufficient, the material has poor crystallinity and uniformity, which affects the specific capacity and cycle performance. Comparative Example 2 does not implement surface modification 1 treatment, the material surface characteristics are not optimized, resulting in a decrease in the first coulombic efficiency and cycle performance. Comparative Example 3 does not perform surface modification 2 treatment, SiO2 nanosheets do not grow on the material surface, which cannot provide better surface protection and lithium ion transmission channels, so the performance is not as good as that of the examples. Comparative Example 4 lacks surface modification 3 treatment, the nanosheet structure on the material surface is not complete, which affects the diffusion of lithium ions and the stability of the material (such as Figure 7 ).

[0075] Comparative Example 5 uses the prior art to prepare a lithium-rich layered positive electrode material, and its various electrochemical performance indicators are weak. This further proves the significant advantages of the preparation method proposed in the present application, especially the microwave reaction and surface modification process, in improving the electrochemical performance of lithium-rich layered positive electrode materials.

[0076] The thermal stability of the material was further tested, and the data are as follows: Table 2 Thermal stability test results Compared with the comparative examples, the peak temperature of the inventive example is increased to above 260℃, indicating that the lithium-rich layered cathode material prepared by the present application has more excellent thermal stability. In the actual application of the battery, thermal stability is a very critical performance indicator. Higher peak temperature means that the material will only react violently at a higher temperature environment, which greatly reduces the risk of safety problems such as thermal runaway, fire, and even explosion caused by overheating of the battery during use. Smaller heat release indicates that the material releases less energy during thermal decomposition, which can reduce the accumulation of heat inside the battery and further protect the safety performance of the battery.

[0077] The peak temperature of the comparative examples is generally low, and the heat release is large, which reflects the poor thermal stability. Comparative examples 1-4 lack some key preparation steps, resulting in defects in the structure and performance of the material, thereby affecting the thermal stability. Comparative example 5 is prepared by using the prior art, and its thermal stability is weak, which again highlights the advantages of the preparation method of the present application.

[0078] In the field of lithium-ion batteries, the thermal stability of the cathode material is directly related to the safety and service life of the battery. The present application effectively improves the thermal stability of the lithium-rich layered cathode material through unique precursor preparation, microwave reaction, high-temperature sintering, and three-step surface modification processes. This not only provides more reliable protection for the widespread application of lithium-ion batteries in electric vehicles, portable electronic devices, and other fields, but also provides new ideas and methods for the research and development of future high-performance battery materials.

[0079] In addition, the thermal stability of the material is also related to the electrochemical performance of the battery. Stable thermal performance helps to maintain the structural integrity of the material, thereby ensuring the stability of the electrochemical performance of the battery during charging and discharging. Therefore, the lithium-rich layered cathode material prepared by the present application has dual advantages in thermal stability and electrochemical performance, making it have broad market application prospects and great commercial value.

[0080] In summary, the preparation method of the lithium-rich layered cathode material provided by the present application can effectively improve the first discharge specific capacity, the first coulombic efficiency, and the cycle performance of the material through a unique process flow, providing a feasible solution for the preparation of high-performance lithium-ion battery cathode materials. Future research can further optimize the process parameters to further improve the electrochemical performance of the material.

[0081] It should be noted that the above embodiments are only part of the preferred modes of implementing the present application, not all. Obviously, based on the above embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor should be within the scope of protection of the present application.

Claims

1. A method for preparing a lithium-rich layered cathode material, characterized in that, The positive electrode material is prepared by co-precipitation method, and then obtained by three-step surface modification, the specific steps are: (1) precursor preparation: first, prepare a 2.0 mol / L metal salt solution by mixing nickel salt, cobalt salt and manganese salt, and prepare a 2 mol / L Na2CO3 solution and a 0.3 mol / L ammonia water solution, then, add the three solutions into a continuously heated and stirred reaction kettle, the pH is 9-11, the stirring speed is 300-800 rpm, the reaction temperature is 50-80℃, the reaction is aged for 40-48h, and then a suspension emulsion A is obtained; (2) microwave reaction: transfer the suspension emulsion A into a high-pressure sealed microwave reaction kettle, then perform microwave heating, and microwave hydrothermal reaction at 190-200℃ and 2-3 MPa for 2-4 hours, cool to room temperature, open the high-pressure reaction kettle, centrifuge the reaction product, wash with water and ethanol alternately for three times, and dry in a vacuum drying oven at 100-110℃ for 10-15 hours to obtain a precursor material B; (3) high-temperature sintering: mix and grind the precursor material B and lithium salt according to a molar ratio of 1.2:1, heat the powder in a muffle furnace at a heating rate of 5℃ / min, first sinter at 400℃ for 4h, and then sinter at 800℃ for 8h to obtain an original lithium-rich manganese-based material C; (4) surface modification 1: dissolve NaBH4 in deionized water to prepare a 2-3 mol / L solution, add the lithium-rich manganese-based material C into the solution, continuously stir for 15-30 min, then filter and place in a vacuum drying oven for 12h, and sinter the dried powder at 350℃ in an argon gas mixed atmosphere containing 5-10% H2 for 3h to obtain a lithium-rich manganese-based material D; (5) surface modification 2: dissolve 0.1 mol / L ethyl silicate TEOS in anhydrous ethanol, add 0.05 mol / L dilute ammonia water, adjust the pH of the system to 9.5-10, and hydrolyze at 40℃ for 30 min to form a transparent SiO2 sol; disperse the lithium-rich manganese-based material D obtained in step 1 into the above sol, and ultrasonic treat for 20-30 min, and continuously stir at 55-60℃ for 3-4h; (6) surface modification 3: transfer the mixture into a hydrothermal kettle, add urea and cetyltrimethylammonium bromide CTAB, heat to 180℃ at a heating rate of 2℃ / min, and keep the temperature for 6h to promote the directional growth of SiO2 on the material surface into nanosheets, and naturally cool down; (7) post-treatment: centrifuge, wash with ethanol for 3 times, vacuum dry at 75-80℃ for 12-15h, and then sinter at 350-400℃ for 2h in N2 atmosphere to obtain the final product, a lithium-rich layered positive electrode material.

2. The method of claim 1, wherein the lithium-rich layered cathode material is prepared by the steps of: preparing a lithium-containing compound; mixing the lithium-containing compound with a transition metal compound; and mixing the lithium-containing compound and the transition metal compound with a lithium source. In step (1), the nickel salt is NiSO4·6H2O, the cobalt salt is CoSO4·7H2O, and the manganese salt is MnSO4·4H2O, and the molar ratio is 15:10:

75.

3. The method for preparing the lithium-rich layered cathode material according to claim 1, wherein: In step (1), the volume ratio of the metal salt solution, the Na2CO3 solution and the ammonia water is 1:1:0.

5.

4. The method for preparing the lithium-rich layered cathode material according to claim 1, wherein: The lithium salt in step (3) is one or more of lithium hydroxide, lithium nitrate or lithium carbonate.

5. The method for preparing the lithium-rich layered cathode material according to claim 1, wherein: The mass ratio of NaBH4 to the lithium-rich manganese-based material C in step (4) is 2:

1.

6. The method for preparing the lithium-rich layered cathode material according to claim 1, wherein: The solid-liquid ratio of the lithium-rich manganese-based material D and the sol in step (5) is 1:50 g / mL, and the volume ratio of ethyl silicate to anhydrous ethanol is 1:

8.

7. The method for preparing the lithium-rich layered cathode material according to claim 1, wherein: The mass ratio of the lithium-rich manganese-based material D, urea and cetyltrimethylammonium bromide CTAB in step (6) is 1:0.3-0.5:0.4.

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