Preparation method and application of alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material

Abstract

The present invention belongs to the technical field of electrode materials, and specifically relates to a preparation method and application of an alkali metal ion-doped sodium vanadium fluorophosphate@carbon composite material. The present invention combines three methods of surface carbon coating modification, morphology modification and metal ion doping modification. The prepared lithium-doped sodium vanadium fluorophosphate or potassium-doped sodium vanadium fluorophosphate is used as a positive electrode material for an aqueous zinc ion battery, which can enable the battery to obtain excellent rate performance and stable cycle performance, while ensuring the structural stability of the battery during long cycles. The present invention adopts a microwave hydrothermal assisted calcination method that is rapid in reaction, low in cost and can be scalable, which can greatly shorten the reaction time and is conducive to improving production efficiency. At the same time, by compounding NVOPF with a nitrogen-carbon material with high electronic conductivity, and doping a metal element at the sodium element site, a high-rate, long-cycle stable nitrogen-carbon composite positive electrode material for an aqueous zinc ion battery can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrode materials, and in particular relates to a preparation method and application of an alkali metal ion-doped sodium vanadium fluorophosphate@carbon composite material. Background Art

[0002] With the development of large-scale energy storage equipment, the demand and requirements for batteries are constantly increasing. Among them, lithium-ion batteries have been widely used in 3C consumer electronics, electric vehicles, and military industries due to their advantages such as high energy density, long service life, low self-discharge rate, and mature preparation process. However, the shortcomings of lithium ions have also been gradually exposed, such as the uneven distribution of lithium resources leading to rising prices, the easy generation of lithium dendrites under overcharging causing battery short circuits, and the toxicity, low ignition point, and poor thermal stability of organic electrolytes. These problems have seriously limited the further application of lithium-ion batteries in the field of large-scale energy storage. Therefore, it is of great significance to the development of human civilization to develop a low-cost, highly safe, and environmentally friendly secondary battery as a candidate for large-scale energy storage power stations to cope with the existing energy crisis.

[0003] Aqueous zinc-ion batteries (AZIBs) are widely favored due to their low cost, high safety and environmental friendliness. Therefore, the successful development and application of AZIBs in the field of safe and efficient large-scale energy storage has become a common goal. The negative electrode of aqueous zinc-ion batteries usually uses metallic zinc, which is due to the good chemical stability and reversibility of metallic zinc in aqueous electrolytes. At the same time, metallic zinc as the negative electrode can provide a high mass specific capacity (820mAh·g -1 ) and volumetric capacity (5855mAh·cm -3 ). And the aqueous electrolyte has a better performance than the organic electrolyte (1~10mS·cm -1 ) Higher ionic conductivity, about 1S·cm -1 High conductivity ensures that the migration dynamics of zinc ions can meet the requirements of higher charge and discharge rates. Furthermore, the aqueous electrolyte has natural flame retardancy, which can meet high safety standards. Furthermore, aqueous zinc-ion batteries can be assembled directly in air, significantly reducing manufacturing and operating costs. Therefore, aqueous zinc-ion batteries are considered a competitive candidate for the next generation of large-scale energy storage power stations.

[0004] At present, since AZIBs are still in the early stages of development, finding suitable zinc storage materials is the key, and cathode materials with zinc storage activity are the top priority. However, there are still the following problems in cathode materials: (1) Zn 2+Large electrostatic interactions can easily lead to large internal stresses during repeated insertion / extraction of the material structure, causing the crystal structure to collapse or even crack the surface, resulting in the inactivation of effective zinc storage sites and reduced capacity and cycle stability; (2) Low electronic conductivity leads to low capacity at high rates; (3) It is easy to induce transition metal dissolution in aqueous electrolytes. Therefore, researching and developing a positive electrode material system that can cope with the above problems is a key step at present. At present, the positive electrode materials with zinc storage activity reported at home and abroad mainly include manganese-based positive electrodes, vanadium-based positive electrodes, Prussian blue analogs and organic materials. Among them, vanadium-based phosphates (M3V2(PO4)3, M=Li, Na, K) have a higher average voltage (>1.15V) due to the presence of [PO4] polyanion groups, and their crystal structure is an open skeleton composed of oxygen atoms shared by [PO4] tetrahedrons and [VO6] octahedrons at the corners, so Na + / Zn 2+ There is enough migration space in the channel, which is also called fast sodium ion conductor structure (NASICON), and the PO bond has high binding energy, which can ensure the structural stability of the material. The above advantages have attracted the attention of many researchers. At the same time, due to its suitable Zn 2+ Vanadium-based phosphates have been widely studied due to their large diffusion channels, good structural stability and high voltage. Compared with Prussian blue analogs, vanadium-based phosphates have higher theoretical capacity, better cycle life and higher rate capacity; compared with manganese-based positive electrode materials, vanadium-based phosphates have a more stable structure, mainly because of the presence of Zn 2+ / H + Repeated insertion and removal of byproducts can easily lead to structural damage of MnO2, which in turn causes material shedding, ultimately resulting in poor cycle stability and significant capacity decay. Furthermore, vanadium-based phosphates are more suitable for aqueous batteries, but Mn dissolves more severely in water, further reducing the active material and battery capacity. However, the low electronic conductivity of NASICON materials affects their rate performance, and vanadium dissolution also reduces cycle stability.

[0005] NVOPF(Na2V6O 163H2O), also known as hydrovanadium, is a layered vanadium oxide with adjustable crystal structure and high capacity. It is currently one of the most widely studied cathode materials. Its high-rate stability and cycle life make it a promising cathode material, promising to promote the application and development of aqueous zinc-ion batteries in the energy storage field. Current research on sodium vanadyl fluorophosphate (NVOPF) as a cathode material for aqueous zinc-ion batteries has often encountered complex, time-consuming, and costly preparation methods, even causing environmental pollution and failing to meet the requirements of large-scale energy storage. For example, NVOPF is currently commonly prepared using a one-step hydrothermal synthesis or a precursor synthesis followed by high-temperature calcination. However, hydrothermal reactions have long synthesis cycles and complex operational steps. Precursor synthesis is commonly performed using methods such as ball milling, hydrothermal / solvothermal methods, electrospinning, and spray drying. Ball milling has the advantages of significantly reducing the reaction activation energy, improving the electrochemical performance of the material, and being simple and amenable to large-scale production. However, its disadvantages include long milling times and high noise levels. The advantage of the hydrothermal method is that it can create a high temperature and high pressure environment in a sealed container, but the disadvantage is that the reaction time is relatively long. The advantages of electrospinning are simple manufacturing equipment, low spinning cost, and controllable process. The disadvantage is that there are toxic solvents in the polymer solution, which not only pollutes the environment and is not conducive to recycling, but also has a low fiber yield. The advantage of the spray drying method is that the drying process is very rapid and the production efficiency is high. The disadvantages are that the equipment is relatively complex, the floor space is large, the one-time investment is too large, the powder recovery device is expensive, the thermal efficiency is not high, and the heat consumption is large. At the same time, although the NVOPF material has good foresight as a high-performance AZIBs positive electrode, its structure itself has Vt 2g The non-bonding orbitals of the electrons result in a large band gap (~2eV) and low electronic conductivity (~10 -7 S cm -1 ), and there is also a solubility problem in aqueous electrolytes, so it is necessary to further modify the NVOPF material to improve its zinc storage performance and stability.

[0006] At present, the modification methods of NVOPF cathode materials mainly include surface carbon coating modification, morphology modification and metal ion doping modification. Among them, surface carbon coating modification is to coat a layer of chemically stable and conductive material on the surface, which is beneficial to improve the transmission path of electrons and ions between material particles, improve the conductivity of the material, and provide a stable chemical and electrochemical reaction interface. Morphology modification is mainly achieved by reducing the particle size and synthesizing spherical, rod-shaped, sheet-shaped, spindle-shaped, micro-nano spherical and other morphologies to increase the specific surface area and active sites of the material, shorten the Na +Transmission distance, thereby improving the conductivity and rate performance of the material. Doping metal ion modification is to dope certain metal ions with good conductivity into the lattice of the material. This method can produce lattice defects or electron holes in the material without changing the crystal structure, thereby effectively and directly improving the intrinsic electronic and ionic conductivity of the material. At present, the surface carbon coating modification method is mainly to coat redox graphene, graphene and amorphous carbon. The morphology modification is mainly nano-sheet and micron sphere modification. The method of doping metal ion modification is mainly to dope metal elements at the vanadium element site, such as Mg 2+ and Mn + However, the NVOPF cathode materials obtained by these current modification methods still have shortcomings such as low conductivity, poor stability, complex process, high cost, and disadvantages for large-scale production. There is an urgent need to develop better optimization and improvement strategies. Summary of the Invention

[0007] In order to overcome the above-mentioned shortcomings of the prior art, the present invention uses a microwave hydrothermal assisted calcination method that is fast in reaction, low in cost and can be scalable to obtain lithium-doped sodium vanadium fluorophosphate (N) by doping lithium or potassium metal elements at the Na site and compounding them with a nitrogen-carbon composite material with high electronic conductivity. 2.85 L 0.15 VOPF@NC) or potassium-doped sodium vanadyl fluorophosphate (N 2.85 K 0.15 VOPF@NC), thereby solving the problem of aqueous electrolyte dissolving the positive electrode while ensuring the integrity of the electrode material and improving the electronic conductivity of the material.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] The first aspect of the present invention provides a method for preparing an alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material, the method comprising the following steps:

[0010] S1. Dissolve vanadyl acetylacetonate in ethanol, and separately dissolve sodium fluoride, ammonium dihydrogen phosphate, and potassium fluoride or lithium fluoride in water. Combine the two solutions and perform a microwave hydrothermal reaction. After the reaction, wash and dry to obtain a precursor.

[0011] S2, dissolving the precursor of step S1, dopamine hydrochloride, trishydroxymethylaminomethane and polyether P123 in water, drying and calcining in an inert gas atmosphere to obtain N 2.85 L 0.15 VOPF@NC or N 2.85 K 0.15 VOPF@NC.

[0012] The microwave hydrothermal method employed in this invention effectively addresses the issues of long production times, high noise levels, low yields, and low thermal conversion efficiency. Advantages of this method include mild conditions, low energy consumption, rapid reaction speed, small and uniform product particle size, light particle agglomeration, and a well-controlled crystal shape. Furthermore, compounding NVOPF with a high-electronic conductivity carbon material and doping it with metal elements can further enhance the material's electronic conductivity.

[0013] Preferably, the temperature of the microwave hydrothermal reaction in S1 is 120-140°C, the heating rate is 7-13°C / min, and the time is 1-3h.

[0014] Preferably, the molar ratio of vanadyl acetylacetonate, sodium fluoride, ammonium dihydrogen phosphate and potassium fluoride or lithium fluoride in S1 is 0.6-0.8:0.9-1.1:0.1-0.2:1.0-1.2.

[0015] Preferably, the mass ratio of the precursor in S2 to dopamine hydrochloride, trishydroxymethylaminomethane and polyether P123 is 100:40:40:16.

[0016] Preferably, the calcination temperature in S2 is 500-700° C. and the calcination time is 6-8 h.

[0017] Preferably, the washing in S1 is to wash the reaction solution with water and ethanol respectively, and then collect the precipitate by high-speed centrifugation 3-7 times.

[0018] More preferably, the rotation speed of the high-speed centrifugation is not less than 6000 r / min.

[0019] The second aspect of the present invention provides an alkali metal ion-doped sodium vanadium oxyfluorophosphate@carbon composite material prepared by the preparation method described in the first aspect.

[0020] The present invention combines three methods: surface carbon coating modification, morphology modification and metal ion doping modification. Among them, a microwave hydrothermal method is used to form NVOPF with small particle size and uniform distribution; a carbon composite material is coated on the surface of NVOPF to improve the conductivity between particles and stabilize its morphology; and a method of sodium element site doping by alkali metal ions can improve the intrinsic electronic and ionic conductivity of the NVOPF material. Therefore, the NVOPF prepared by the method of the present invention is 2.85 L 0.15 VOPF@NC or N 2.85 K 0.15 As a cathode material for aqueous zinc-ion batteries, VOPF@NC can enable the battery to achieve excellent rate performance and stable cycle performance, while ensuring the structural stability of the battery during long cycles.

[0021] The third aspect of the present invention provides the use of the alkali metal ion-doped sodium vanadium fluorophosphate@carbon composite material described in the second aspect in the preparation of a positive electrode material for an aqueous zinc ion battery.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention adopts vanadyl acetylacetonate as a vanadium source, sodium fluoride as a sodium source and a fluorine source, ammonium dihydrogen phosphate as a phosphate source, and potassium fluoride or lithium fluoride as a doping source. After mixing the raw materials, the mixture is rapidly reacted by microwave hydrothermal method to obtain a precursor. The precursor is then dissolved in water with dopamine hydrochloride, trishydroxymethylaminomethane and polyether P123, and the mixture is dried and calcined at high temperature under inert gas condition to obtain lithium-doped sodium vanadyl fluorophosphate (N 2.85 L 0.15 VOPF@NC) or potassium-doped sodium vanadyl fluorophosphate (N 2.85 K 0.15 VOPF@NC), through fullprof refinement of its XRD data, it was found that K ions and Na ions doped at the Na site can obtain good refinement factors, indicating that K ions or Li ions are doped at the Na site. 2.85 L 0.15 VOPF@NC or N 2.85 K 0.15 As a cathode material for aqueous zinc-ion batteries, VOPF@NC can enable the battery to achieve excellent rate performance and stable cycle performance, while ensuring the structural stability of the battery during long cycles.

[0024] The present invention utilizes a microwave hydrothermal assisted calcination method that is rapid, low-cost, and scalable, significantly shortening the reaction time and improving production efficiency. Furthermore, by combining NVOPF with a nitrogen-carbon material with high electronic conductivity and doping metal elements at the sodium site, the electronic conductivity of the material is enhanced both in the bulk and on the surface, resulting in a high-rate, long-cycle stable nitrogen-carbon composite cathode material for aqueous zinc-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 N 2.85 L 0.15 X-ray diffraction spectrum of VOPF@NC (top) and schematic spectrum refined by fullprof (bottom);

[0026] Figure 2 N 2.85 L 0.15 Scanning electron microscopy image of VOPF@NC;

[0027] Figure 3 N2.85 L 0.15 Rate performance of VOPF@NC as a cathode material for aqueous zinc-ion batteries at current densities of 0.5-30C;

[0028] Figure 4 N 2.85 L 0.15 Cycling performance of VOPF@NC as a cathode material for aqueous zinc-ion batteries after activation for 5 cycles at a current density of 0.5-30C and then at a current density of 30C;

[0029] Figure 5 N 2.85 L 0.15 Scanning electron micrograph of VOPF@NC as the cathode material for aqueous zinc-ion batteries after 50 cycles at a current density of 0.5-30C;

[0030] Figure 6 N 2.85 K 0.15 X-ray diffraction spectrum of VOPF@NC (top) and schematic spectrum refined by fullprof (bottom);

[0031] Figure 7 N 2.85 K 0.15 Scanning electron microscopy image of VOPF@NC;

[0032] Figure 8 N 2.85 K 0.15 Rate performance of VOPF@NC as a cathode material for aqueous zinc-ion batteries at current densities of 1-30C;

[0033] Figure 9 N 2.85 K 0.15 Cycling performance of VOPF@NC as a cathode material for aqueous zinc-ion batteries after activation at a current density of 1C for 10 cycles and then at a current density of 20C;

[0034] Figure 10 N 2.85 K 0.15 Scanning electron micrograph of VOPF@NC as the cathode material for aqueous zinc-ion batteries after 50 cycles at a current density of 1C;

[0035] Figure 11 is the X-ray diffraction spectrum of NVOPF;

[0036] Figure 12 is the scanning electron microscope image of NVOPF;

[0037] Figure 13This is the rate performance diagram of NVOPF as the positive electrode material of aqueous zinc-ion batteries at a current density of 1-30C;

[0038] Figure 14 This is the cycling performance diagram of NVOPF as the positive electrode material for aqueous zinc-ion batteries at a current density of 20C after activation for 10 cycles at a current density of 1C;

[0039] Figure 15 This is a scanning electron microscope image of NVOPF as the positive electrode material for aqueous zinc-ion batteries after 50 cycles at a current density of 1C. DETAILED DESCRIPTION

[0040] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0041] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0042] Example 1: Lithium-doped sodium vanadium fluorophosphate (N 2.85 Li 0.15 Preparation of VOPF@NC) and its application as cathode material for aqueous zinc-ion batteries

[0043] 1. N 2.85 Li 0.15 Preparation of VOPF@NC:

[0044] 1.019mmol sodium fluoride (NaF), 0.15mmol lithium fluoride (LiF) and 1.05mmol ammonium dihydrogen phosphate (NH4H2PO4) were stirred and dissolved in 12mL of deionized water, and 0.7mmol of acetylacetonatovanadium (C 10 H 14O5V) was stirred and dissolved in 24mL of anhydrous ethanol. After combining the two solutions, stirring was continued and 18mL of deionized water was added to ensure the pressure of the reactor. The obtained mixed solution was then placed in a polytetrafluoroethylene liner, and the temperature was raised from room temperature to 130°C by microwave-assisted heating at a heating rate of 10°C / min, and kept at 130°C for 1h. After the reaction, the reaction solution was cleaned with deionized water and anhydrous ethanol by high-speed centrifugation (6000r / min) three times, and the precipitate was collected and placed in a 60°C drying oven for 10h to obtain the precursor after complete drying. Then 100mg of the precursor, 40mg of dopamine hydrochloride, 40mg of trihydroxymethylaminomethane and 16mg of polyether P123 were weighed and added to 100mL of deionized water, stirred for 12h until dissolved, then filtered and dried in a 60°C oven for 12h. Finally, the obtained product was placed in a tubular furnace with argon and calcined at 600°C for 7h to obtain N 2.85 Li 0.15 VOPF@NC.

[0045] like Figure 1 As shown, the N prepared in this embodiment 2.85 Li 0.15 The peak positions and peak intensities of the X-ray diffraction spectrum of VOPF@NC correspond to those of the standard card, with no other impurity peaks and sharp peaks, indicating that the purity and crystallinity of the material are good. At the same time, through fullprof refinement of its XRD data, it was found that Li ion doping at the Na position can obtain a good refinement factor, indicating that Li ion doping at the Na position. Figure 2 As shown, the N prepared in this embodiment 2.85 Li 0.15 The particle size of VOPF@NC is 40-70nm.

[0046] 2. The N obtained in this embodiment 2.85 Li 0.15 VOPF@NC is used as a cathode material in aqueous zinc-ion batteries. The specific implementation method is as follows:

[0047] The above N 2.85 Li 0.15 VOPF@NC was ground with conductive carbon black and sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 7:2:1, and an appropriate amount of deionized water was added to form a uniform, fine slurry. The slurry was then evenly coated onto a 12mm diameter stainless steel mesh and dried in an oven at 60°C for 12 hours. Finally, a button cell was assembled using the stainless steel mesh loaded with active material as the positive electrode and zinc metal as the negative electrode. Charge and discharge tests were conducted within a voltage window of 0.4-1.9V.

[0048] Test the N prepared in this embodiment 2.85 Li0.15 VOPF@NC as a cathode material for aqueous zinc-ion batteries has a high rate performance at current densities of 0.5, 1, 2, 5, 10, 20, and 30C. Figure 3 As shown, the battery provides 147.4, 140.4, 128.9, 113.4, 93.4, and 70 mAh g at different current densities. -1 When the current density returns to 0.1A g -1 The test battery provides a charge capacity of 155 mAh g -1 Compared with the first week, the capacity retention rate is 105%, which shows excellent rate performance.

[0049] Test the N prepared in this example 2.85 Li 0.15 The cycling performance of VOPF@NC as the cathode material for aqueous zinc-ion batteries after activation at 0.5C for 5 cycles and then at 30C. Figure 4 As shown in the figure, the first week charge capacity of the battery is 54.1 mAh g -1 After 4000 cycles, the charge capacity provided is 47.2 mAh g -1 , showing stable cycling performance.

[0050] The N prepared in this example 2.85 Li 0.15 SEM scan of VOPF@NC as the cathode material of aqueous zinc-ion battery after 50 cycles at 0.5C. Figure 5 As shown, it can be found that the morphology of the positive electrode material is well maintained, indicating that carbon coating can stabilize the structure of the material and prevent the positive electrode from dissolving.

[0051] Example 2: Potassium-doped sodium vanadium fluorophosphate (N 2.85 K 0.15 Preparation of VOPF@NC) and its application as cathode material for aqueous zinc-ion batteries

[0052] 1. N 2.85 K 0.15 Preparation of VOPF@NC:

[0053] 1.019mmol sodium fluoride (NaF), 0.15mmol lithium fluoride (KF) and 1.05mmol ammonium dihydrogen phosphate (NH4H2PO4) were stirred and dissolved in 12mL of deionized water, and 0.7mmol of acetylacetonatovanadium (C 10 H 14O5V) was stirred and dissolved in 24mL of anhydrous ethanol. After combining the two solutions, stirring was continued and 18mL of deionized water was added to ensure the pressure of the reactor. The obtained mixed solution was then placed in a polytetrafluoroethylene liner, and the temperature was raised from room temperature to 130°C by microwave-assisted heating at a heating rate of 10°C / min, and kept at 130°C for 1h. After the reaction, the reaction solution was cleaned with deionized water and anhydrous ethanol respectively, and centrifuged at high speed (6000r / min) three times. The precipitate was collected and placed in a 60°C drying oven for 10h to obtain the precursor after complete drying. Then 100mg of the precursor, 40mg of dopamine hydrochloride, 40mg of trihydroxymethylaminomethane and 16mg of polyether P123 were weighed and added to 100mL of deionized water, stirred for 12h until dissolved, then filtered and dried in a 60°C oven for 12h. Finally, the obtained product was placed in a tubular furnace with argon and calcined at 600°C for 7h to obtain N 2.85 K 0.15 VOPF@NC.

[0054] like Figure 6 As shown, the N prepared in this embodiment 2.85 K 0.15 The peak positions and peak intensities of the X-ray diffraction spectrum of VOPF@NC correspond to those of the standard card, with no other impurity peaks and sharp peaks, indicating that the purity and crystallinity of the material are good. At the same time, through fullprof refinement of its XRD data, it was found that K ion doping at the Na position can obtain a good refinement factor, indicating that K ion doping at the Na position. Figure 7 As shown, the N prepared in this embodiment 2.85 K 0.15 The particle size of VOPF@NC is 40-70nm.

[0055] The N obtained in this example 2.85 K 0.15 VOPF@NC is used as a cathode material in aqueous zinc-ion batteries. The specific implementation method is as follows:

[0056] The above N 2.85 K 0.15 VOPF@NC was ground with conductive carbon black and sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 7:2:1, and an appropriate amount of deionized water was added to form a uniform, fine slurry. The slurry was then evenly coated onto a 12mm diameter stainless steel mesh and dried in an oven at 60°C for 12 hours. Finally, a button cell was assembled using the stainless steel mesh loaded with active material as the positive electrode and zinc metal as the negative electrode. Charge and discharge tests were conducted within a voltage window of 0.4-1.9V.

[0057] Test the N prepared in this embodiment 2.85 K 0.15The rate performance of VOPF@N as a cathode material for aqueous zinc-ion batteries at current densities of 1, 2, 5, 10, 20, and 30C. Figure 8 As shown, the battery provides 125, 121.4, 113.7, 99.1, 78.8, and 62.9 mAh g at different current densities. -1 When the current density returns to 0.1A·g -1 The charge capacity provided by the test battery is 134mAh·g -1 Compared with the first week, the capacity retention rate is 107%, which shows excellent rate performance.

[0058] Test the N prepared in this example 2.85 K 0.15 The cycling performance of VOPF@NC as the cathode material for aqueous zinc-ion batteries after activation at 1C for 10 cycles and then at 20C. Figure 9 As shown in the figure, the first week charge capacity of the battery is 66.8 mAh g -1 After 4000 cycles, the charge capacity provided is 53.3 mAh g -1 , showing stable cycling performance.

[0059] The N prepared in this example 2.85 K 0.15 SEM scan of VOPF@NC as the cathode material for aqueous zinc-ion batteries after 50 cycles at 1C. Figure 10 As shown, it can be found that the morphology of the positive electrode material is well maintained, indicating that carbon coating can stabilize the structure of the material and prevent the positive electrode from dissolving.

[0060] Comparative Example 1: Preparation of NVOPF and its application as a positive electrode material for aqueous zinc ion batteries

[0061] 1. Preparation of NVOPF:

[0062] 1.169mmol sodium fluoride (NaF) and 1.05mmol ammonium dihydrogen phosphate (NH4H2PO4) were stirred and dissolved in 12mL deionized water, and 0.7mmol acetylacetonatovanadium (C 10 H 14O5V) was stirred and dissolved in 24mL of anhydrous ethanol. After combining the two solutions, stirring was continued and 18mL of deionized water was added to ensure the pressure of the reactor. The obtained mixed solution was then placed in a polytetrafluoroethylene liner, and the temperature was raised from room temperature to 130°C by microwave-assisted heating at a heating rate of 10°C / min, and kept at 130°C for 1h. After the reaction, the reaction solution was washed with deionized water and anhydrous ethanol respectively, and centrifuged at high speed (6000r / min) three times. The precipitate was collected and placed in a 60°C drying oven for 10h. After complete drying, a precursor was obtained. Finally, the obtained precursor was placed in an argon tube furnace and calcined at 600°C for 7h to obtain the product, which was recorded as: NVOPF.

[0063] like Figure 11 As shown in the figure, the peak position and peak intensity of the X-ray diffraction spectrum of the prepared NVOPF correspond to those of the standard card, with no other impurity peaks and sharp peaks, indicating that the purity and crystallinity of the material are good. Figure 12 As shown, the particle size of the prepared NVOPF is 30-60 nm.

[0064] 2. The obtained NVOPF is applied as a cathode material in aqueous zinc ion batteries. The specific implementation method is as follows:

[0065] The NVOPF was ground with conductive carbon black and sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 7:2:1, and an appropriate amount of deionized water was added to form a uniform and fine slurry. The slurry was then evenly coated onto a 12mm diameter stainless steel mesh and dried in an oven at 60°C for 12 hours. Finally, a button cell was assembled using the stainless steel mesh loaded with active material as the positive electrode and zinc metal as the negative electrode. Charge and discharge tests were conducted within a voltage window of 0.4-1.9V.

[0066] The prepared NVOPF was tested as a positive electrode material for aqueous zinc ion batteries at a current density of 1, 2, 5, 10, 20, and 30C. Figure 13 As shown, the battery provides 121.4, 75.3, 57.6, 41.3, 30.5, and 28.8 mAh g at different current densities. -1 When the current density returns to 1C, the charge capacity provided by the test battery is 80.6mAh·g -1 Compared with the first week, the capacity retention rate is 66%, and the rate performance is average.

[0067] The prepared NVOPF was tested as a positive electrode material for aqueous zinc ion batteries after being activated at 1C for 10 cycles and then at 20C. Figure 14 As shown in the figure, the first week charge capacity of the battery is 44.1 mAh g -1, it cannot cycle 4000 times, and its cycle performance is relatively weak.

[0068] The prepared NVOPF was used as the positive electrode material for aqueous zinc ion batteries and then cycled 50 times at 1C and subjected to SEM scanning. Figure 15 As shown, it can be found that flaky byproducts have grown on the positive electrode material.

[0069] In summary, the present invention uses a microwave hydrothermal assisted calcination method that is fast, low-cost and scalable to dope lithium or potassium metal elements at the Na site, and composites NVOPF with a nitrogen-carbon composite material with high electronic conductivity to obtain N 2.85 L 0.15 VOPF@NC or N 2.85 K 0.15 VOPF@NC solves the problem of aqueous electrolyte dissolving the positive electrode while ensuring the integrity of the electrode material, and improves the electronic conductivity of the material, thereby obtaining a high-rate, long-cycle stable nitrogen-carbon composite aqueous zinc-ion battery positive electrode material.

[0070] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A method for preparing an alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material, characterized in that: The following steps are involved: S1. Dissolve vanadyl acetylacetonate in ethanol, and separately dissolve sodium fluoride, ammonium dihydrogen phosphate, and potassium fluoride or lithium fluoride in water. Combine the two solutions and perform a microwave hydrothermal reaction. After the reaction, wash and dry to obtain a precursor. The microwave hydrothermal reaction temperature is 120-140°C, the heating rate is 7-13°C / min, and the reaction time is 1-3 h. The molar ratio of the vanadyl acetylacetonate, sodium fluoride, ammonium dihydrogen phosphate, and potassium fluoride or lithium fluoride is 0.6-0.8:0.9-1.1:0.1-0.2:1.0-1.

2. S2. Dissolve the precursor of step S1, dopamine hydrochloride, trishydroxymethylaminomethane and polyether P123 in water, dry and calcine in an inert gas atmosphere to obtain lithium-doped sodium vanadyl fluorophosphate or potassium-doped sodium vanadyl fluorophosphate.

2. The method for preparing an alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material according to claim 1, characterized in that: The mass ratio of the precursor S2 to dopamine hydrochloride, trishydroxymethylaminomethane and polyether P123 is 100:40:40:

16.

3. The method for preparing an alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material according to claim 1, characterized in that: The calcination temperature in S2 is 500-700° C. and the calcination time is 6-8 h.

4. The method for preparing an alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material according to claim 1, characterized in that: The washing in S1 is to wash the reaction solution with water and ethanol respectively, and then high-speed centrifugation 3-7 times to collect the precipitate.

5. The method for preparing an alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material according to claim 4, characterized in that: The rotation speed of the high-speed centrifuge is not less than 6000 r / min.

6. Alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the alkali metal ion-doped sodium vanadyl fluorophosphate@carbon composite material according to claim 6 in preparing a positive electrode material for an aqueous zinc ion battery.

Images