Nfpp nanosheet-coated layered oxide positive electrode material and preparation method and application thereof

Abstract

The application relates to a kind of NFPP nanosheet coated layered oxide positive electrode materials and its preparation method and application, and relates to the field of sodium ion battery;The preparation method of the NFPP nanosheet coated layered oxide positive electrode material comprises the following steps: dispersing layered transition metal oxide and sodium iron pyrophosphate nanosheet in solvent, adding F, N-containing complex carbon source after reaction;The mixture is annealed under the condition of inert atmosphere, 350-600 DEG C.The in-situ carbonization of the application is closely combined between NFPP and layered oxide, and a layered oxide composite positive electrode material with core-shell structure is formed.The contact between layered oxide positive electrode material and electrolyte is effectively avoided, and the occurrence of side reaction is reduced.The carbon-coated layer of NFPP is doped with fluorine and nitrogen elements, which can improve the conductivity and interface stability of the carbon-coated layer;The finally obtained layered oxide composite positive electrode material has good structural stability, excellent long cycle performance and excellent rate performance.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery technology, and in particular to an NFPP nanosheet-coated layered oxide cathode material, its preparation method, and its application. Background Technology

[0002] Currently, sodium-ion battery cathode materials mainly fall into several categories, including transition metal oxides (such as NaMnO2), polyanionic compounds (such as Na3V2(PO4)3), Prussian materials (such as Na2Fe2(SO4)3), and amorphous materials. Among these, layered transition metal oxides possess high theoretical specific capacity, diverse compositions, and simple synthesis, giving them certain advantages as sodium storage materials. However, layered transition metal oxide cathode materials suffer from poor electrochemical stability; their structure is prone to collapse, severely impacting the battery's cycle life.

[0003] As research and development of sodium-ion batteries continues, the industry has implemented numerous improvements to the performance of layered transition metal oxide cathode materials. For example, patent CN117712356A discloses a core-shell type sodium-ion battery cathode material and its preparation method. The prepared polyanion-coated layered oxide composite material can improve cycle performance and high-temperature storage. However, this invention uses solid-state sintering to prepare the polyanion material and combines it with the layered oxide through physical mixing, which cannot guarantee the consistency of the polyanion material particles or the uniformity of the coating. Furthermore, the coating layer content in this patent is 5-30%, which reduces the material capacity. Patent CN119581537A fuses the internal core material of the layered oxide with the external coating material of the polyanion system through mechanical fusion, obtaining a cathode material with a core-shell structure of layered oxide and polyanion composite. However, mechanical fusion cannot guarantee effective bonding between the polyanion material and the layered oxide, posing a risk of polyanions detaching from the layered oxide material, and it cannot completely prevent side reactions between the layered oxide and the electrolyte. Patent CN118231592A discloses a core-shell structured high-entropy cathode material, its preparation method, and its applications. This invention uses a spray drying method combined with high-temperature sintering at 700-1000℃ to coat phosphate polyanions onto the surface of a layered oxide. The resulting composite material significantly improves its rate performance. However, the high-temperature sintering at 700-1000℃ causes the coating particles to grow excessively large, reducing the specific surface area and negatively impacting Na+ efficiency. + Insertion and deintercalation. Therefore, developing a layered oxide sodium-ion battery cathode material that simultaneously achieves high capacity, long lifespan, and high rate capability is of great significance. Summary of the Invention

[0004] Based on this, in order to address the shortcomings of existing layered oxide sodium-ion battery cathode materials, a method for preparing layered oxide cathode materials coated with sodium iron phosphate pyrophosphate (NFPP) nanosheets is provided; the prepared material has good structural stability, long cycle performance and rate performance.

[0005] Another objective of this invention is to provide an NFPP nanosheet-coated layered oxide cathode material.

[0006] Another objective of this invention is to provide an application of the above-mentioned NFPP nanosheet-coated layered oxide cathode material in the preparation of sodium-ion batteries.

[0007] This invention discloses a method for preparing an NFPP nanosheet-coated layered oxide cathode material, comprising the following steps:

[0008] S1, layered transition metal oxides and sodium iron phosphate nanosheets are dispersed in a solvent, a complexed carbon source containing F and N is added and a coordination reaction is carried out, and the mixture is dried to obtain a mixture.

[0009] S2, the mixture is annealed in an inert atmosphere at 350-600°C to obtain F and N co-doped NFPP nanosheet-coated layered oxide cathode material.

[0010] In the preparation method of NFPP nanosheet-coated layered oxide cathode material of the present invention, NFPP is coordinated and bound to the surface of layered transition metal oxide in a dispersion system using a complex carbon source containing F and N. After low-temperature annealing, the complex carbon source is carbonized in situ to obtain N / F co-doped NFPP@C / layered oxide cathode material. This anchors NFPP to the surface of layered transition metal oxide, preventing cracking and shedding of the layered oxide crystal particles and dissolution of the transition metal, effectively avoiding contact between the layered oxide cathode material and the electrolyte, and reducing the occurrence of side reactions. At the same time, F and N are introduced to improve interfacial stability and conductivity.

[0011] Furthermore, the NFPP, acting as a shell, possesses a three-dimensional framework structure that provides a broad tunneling network for sodium ion transport. During charge and discharge, a single-phase solid solution reaction occurs, effectively suppressing structural collapse or phase transitions. This allows for stable operation over a wide voltage range, reducing electrode material breakage and failure, and extending battery cycle life. Simultaneously, the NFPP nanosheets have a larger specific surface area, providing more active sites for sodium ion transport. + Intercalation and deintercalation significantly improve the conductivity of the layered oxide composite material itself. This results in a layered oxide composite cathode material that possesses good structural stability, excellent long-cycle performance, and outstanding rate performance.

[0012] It should be noted that the annealing temperature in this invention should be controlled within the range of 350-600℃. Excessive carbonization temperature can lead to cracks in the carbon layer, causing N / F elements to be released in a gaseous state (e.g., ...). HF causes a sharp drop in doping concentration; excessively high temperatures can even lead to lattice collapse in the NFPP coating layer, transforming its layered structure into an amorphous phase, Na + Blocked diffusion channels can also generate impurity phases, severely affecting the effectiveness of the coating layer.

[0013] Preferably, the solvent is an ethanol-water solution in any proportion.

[0014] In some embodiments, the coordination reaction is carried out at a temperature of 45-75°C.

[0015] In some embodiments, in step S1, the mass ratio of sodium iron phosphate pyrophosphate nanosheets to layered transition metal oxides is (0.01-0.1):1.

[0016] In some embodiments, the layered transition metal oxide has the chemical formula NaMO2, where M is selected from at least one of Mn, Fe, Cu, Ti, Ni, V, Co, Mg, Nb, Al, or Zn.

[0017] In some embodiments, the chemical formula of the sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7.

[0018] In some embodiments, in step S1, the molar ratio of F to N in the F- and N-containing complexed carbon source is (1-3):(1-3). Optionally, the molar ratio of F to N in the F- and N-containing complexed carbon source can be any one of 1:3, 1:2, 1:1, 1:2, or 1:3, or any range between both.

[0019] In some embodiments, in step S1, the complexing agent is at least one of trifluoroethylamine, a complex of ethylenediaminetetraacetic acid (EDTA) and ammonium fluoride, or a complex of polyvinylidene fluoride (PVDF) and urea. Preferably, in the EDTA and ammonium fluoride complex, the mass ratio of EDTA to ammonium fluoride is 1:(1-4).

[0020] In some embodiments, the complexing agent has a mass fraction of 5-25 wt%.

[0021] In some embodiments, the method for preparing sodium iron phosphate pyrophosphate nanosheets includes the following steps: mixing a phosphorus source, an iron source and a sodium source, adding a template agent and reacting the mixture hydrothermally under alkaline conditions to obtain sodium iron phosphate pyrophosphate nanosheets.

[0022] In some embodiments, the hydrothermal reaction conditions are: reaction temperature 150-200°C, reaction time 6-12h.

[0023] In some embodiments, the molar ratio of P to Fe in the phosphorus source and iron source is (0.75-2.2):1.

[0024] In some embodiments, the sodium source is added in excess. Preferably, the molar ratio of Na to Fe in the sodium and iron sources is >4 / 3. More preferably, the molar ratio of Na to Fe is (2-20):1.

[0025] Preferably, the iron source is selected from at least one of ferrous phosphate, ferrous sulfate, ferrous chloride, ferric chloride, ferrous nitrate, ferrous oxalate, ferric nitrate, or ferric phosphate.

[0026] Preferably, the phosphorus source is selected from at least two of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0027] Preferably, the sodium source is selected from sodium carbonate and / or sodium hydroxide.

[0028] Preferably, the template agent is selected from at least one of cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP), or polyethylene glycol 2000 (PEG-2000).

[0029] This invention discloses an NFPP nanosheet-coated layered oxide cathode material, which is prepared by the method for preparing the NFPP nanosheet-coated layered oxide cathode material.

[0030] This invention relates to the application of the NFPP nanosheet-coated layered oxide cathode material in the preparation of sodium-ion batteries. Compared with existing technologies, the advantages of this invention are:

[0031] This invention provides a method for preparing NFPP nanosheet-coated layered oxide cathode materials, capable of producing F and N co-doped NFPP nanosheet-coated layered oxide cathode materials with a core-shell structure. The surface-coated NFPP nanosheets prevent cracking and shedding of the layered oxide crystal particles and dissolution of transition metals, effectively avoiding contact between the layered oxide cathode material and the electrolyte, and reducing the occurrence of side reactions. Furthermore, the carbon coating layer of NFPP is doped with fluorine and nitrogen, which improves the conductivity and interfacial stability of the carbon coating layer; thus, the final layered oxide composite cathode material possesses good structural stability, excellent long-cycle performance, and outstanding rate performance. Attached Figure Description

[0032] Figure 1 The graphs show the capacity decay curves of the NFPP nanosheet-coated layered oxide cathode materials in various embodiments of the present invention under 1C cycling. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0034] Example 1

[0035] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0036] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0037] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04 O2 (average particle size 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0038] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 500°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0039] Example 2

[0040] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0041] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 150°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0042] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04 O2 (average particle size 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0043] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 500°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0044] Example 3

[0045] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0046] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0047] (2) Weigh 0.02g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04O2 (average particle size 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0048] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 500°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0049] Example 4

[0050] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0051] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0052] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04 O2 (with an average particle size of 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 10 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0053] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 500°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0054] Example 5

[0055] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0056] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed in a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0057] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04 O2 (average particle size 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0058] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 350°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0059] Example 6

[0060] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0061] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0062] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04O2 (average particle size 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% EDTA and NH4F (molar ratio 1:1) composite system was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0063] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 500°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0064] Example 7

[0065] A sodium-ion battery, the manufacturing process of which includes the following steps:

[0066] (1) The positive electrode material, PVDF and conductive carbon black obtained in Example 1 were added to N-methylpyrrolidone solvent in a mass ratio of 95:2:3 to obtain a positive electrode slurry with a solid content of 58%. The slurry was coated, rolled and die-cut to obtain a positive electrode sheet.

[0067] Hard carbon anode material, conductive carbon black and SBR+CMC are mixed in water at a mass ratio of 93:4:3 to obtain anode slurry with a solid content of 45%. The slurry is then coated, rolled and die-cut to obtain anode sheet.

[0068] (2) Assemble the positive electrode, negative electrode and separator, inject electrolyte, perform capacity separation and formation to obtain the sodium-ion battery.

[0069] Comparative Example 1

[0070] A layered oxide cathode material, which differs from Example 1 in that: this comparative example has not undergone NFPP nanosheet coating treatment.

[0071] Comparative Example 2

[0072] A method for preparing a positive electrode material includes the following steps:

[0073] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0074] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04 O2 (with an average particle size of 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed five times with deionized water and anhydrous ethanol to obtain a washing product. The washing product was then dried in an oven at 80 °C for 10 h to obtain the cathode material.

[0075] Comparative Example 3

[0076] A method for preparing an NFPP nanosheet-coated layered oxide cathode material includes the following steps:

[0077] (1) Under magnetic stirring, a phosphorus source (ammonium dihydrogen phosphate and diammonium hydrogen phosphate in a molar ratio of 2:1) and an iron source (ferric nitrate) were mixed at a molar ratio of 2:1 to prepare an aqueous solution with a total concentration of 0.6 mol / L. Then, 0.3 wt% CTAB was added. After the CTAB was evenly dispersed, excess NaOH was added to the dispersion to adjust the pH to 9.5. The dispersion was transferred to a reaction vessel and reacted at 180°C for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was washed five times with water and ethanol and then dried to obtain two-dimensional nanoscale sheet-like NFPP.

[0078] (2) Weigh 0.05g of NFPP and 1g of layered oxide (NaNi) 0.3 Fe 0.33 Mn 0.33 Zn 0.04 O2 (average particle size 6 μm) was dispersed in 100 ml of ethanol aqueous solution, and then 20 wt% trifluoroethylamine was added. The mixture was ultrasonically dispersed for 30 min to obtain a dispersion. The dispersion was then placed in a water bath at 55 °C for 2 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and anhydrous ethanol to obtain the washing product.

[0079] (3) The washing product was dried in an oven at 80°C for 10 hours and then annealed at 750°C for 6 hours under Ar atmosphere to obtain F and N co-doped NFPP@C / layered oxide composite cathode material.

[0080] Comparative Example 4

[0081] A method for preparing an NFPP nanosheet-coated layered oxide cathode material differs from Example 1 in that no complexing agent is added in this comparative example.

[0082] Comparative Example 5

[0083] A method for preparing an NFPP nanosheet-coated layered oxide cathode material differs from Example 1 in that the complexing agent in this comparative example is urea.

[0084] Comparative Example 6

[0085] A method for preparing an NFPP nanosheet-coated layered oxide cathode material differs from Example 1 in that the complexing agent in this comparative example is polyvinylidene fluoride.

[0086] Performance testing

[0087] The cathode materials of Examples 1-6 and Comparative Examples 1-4 were prepared into sodium-ion batteries according to the method of Example 7, and the following performance tests were performed;

[0088] 1. Cyclic performance: Under 45℃ conditions, perform 1.5V-3.9V, 1C cycling, and record the number of cycles when the capacity is less than 80% SOH.

[0089] 2. Rate performance and charge / discharge performance: After fully charging the lithium-ion battery at a constant current and constant voltage of 0.2C, it was discharged at 15C, and its capacity retention was tested. The test results are as follows: Figure 1 As shown in Table 1.

[0090] Table 1

[0091] Example 1 2800 92 Example 2 2200 85 Example 3 2300 84 Example 4 3200 88 Example 5 2200 83 Example 6 2750 91 Comparative Example 1 1500 80 Comparative Example 2 500 45 Comparative Example 3 2100 83 Comparative Example 4 1800 79 Comparative Example 5 2000 85 Comparative Example 6 1900 86

[0092] As can be seen from Table 1, the cathode material of the present invention achieves a 1C cycle performance of over 2200 cycles and a capacity retention rate of over 82% at a 15C rate.

[0093] Compared to Example 1, the material in Comparative Example 1 that was not coated with NFPP nanosheets showed a significant decrease in cycle performance.

[0094] In Comparative Example 2, which was not annealed, its cycle performance and rate performance decreased.

[0095] The annealing temperature in Comparative Example 3 was too high, which to some extent caused cracks in the carbon layer, affecting the effect of the coating layer and reducing the cycle performance and rate performance.

[0096] In Comparative Examples 4-6, the cycling performance and rate performance decreased when no complexing agent was added or the complexing agent contained no F or N.

[0097] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an NFPP nanosheet-coated layered oxide cathode material, characterized in that, Includes the following steps: S1, layered transition metal oxides and sodium iron phosphate nanosheets are dispersed in a solvent, a complexed carbon source containing F and N is added and a coordination reaction is carried out, and the mixture is dried to obtain a mixture. S2, the mixture is annealed in an inert atmosphere at 350-600°C to obtain F and N co-doped NFPP nanosheet-coated layered oxide cathode material.

2. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 1, characterized in that, The chemical formula of the layered transition metal oxide is NaMO2, and M is selected from at least one of Mn, Fe, Cu, Ti, Ni, V, Co, Mg, Nb, Al or Zn.

3. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 1 or 2, characterized in that, In step S1, the mass ratio of the sodium iron pyrophosphate nanosheets to the layered transition metal oxide is (0.01-0.1):

1.

4. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 1, characterized in that, The molar ratio of F to N in the F- and N-containing complexed carbon source is (1-3):(1-3).

5. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 4, characterized in that, In step S1, the F- and N-containing complexed carbon source is selected from at least one of trifluoroethylamine, a complex of ethylenediaminetetraacetic acid and ammonium fluoride, or a complex of polyvinylidene fluoride and urea.

6. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 1, 4, or 5, characterized in that, The complexed carbon source accounts for 5-25 wt% of the mass fraction of the layered transition metal oxide.

7. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 1, characterized in that, The method for preparing sodium iron phosphate pyrophosphate nanosheets includes the following steps: mixing a phosphorus source, an iron source and a sodium source, adding a template agent and reacting the mixture hydrothermally under alkaline conditions to obtain sodium iron phosphate pyrophosphate nanosheets.

8. The method for preparing NFPP nanosheet-coated layered oxide cathode material according to claim 7, characterized in that, The conditions for the hydrothermal reaction are: reaction temperature 150-200℃, reaction time 6-12h.

9. An NFPP nanosheet-coated layered oxide cathode material, characterized in that, It is prepared by the method of any one of claims 1-8 for the preparation of NFPP nanosheet-coated layered oxide cathode material.

10. The application of the NFPP nanosheet-coated layered oxide cathode material of claim 9 in the preparation of sodium-ion batteries.

Images