Preparation method for composite iron-based polyanion positive electrode material

Abstract

A preparation method for a composite iron-based polyanion positive electrode material. The structural formula of the positive electrode material is represented as Na4Fe3(PO4)2(P2O7)@C&MXenes, and the positive electrode material is sodium iron phosphate pyrophosphate compositely coated with an MXenes material and a carbonaceous precursor. The preparation method comprises: weighing a sodium source, a ferrous source, a phosphorus source and a carbon source according to a stoichiometric ratio, uniformly mixing same, and subjecting the mixture to grinding, spray-drying and high-temperature sintering, so as to obtain the composite iron-based polyanion positive electrode material, wherein the carbon source comprises a polyethylene glycol doped with iron and nickel.

Description

A method for preparing composite iron-based polyanionic cathode materials Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material preparation technology, and specifically relates to a method for preparing composite iron-based polyanion cathode materials. Background Technology

[0002] Currently, the sodium-ion battery industry is in the early stages of commercialization, making the search for suitable battery materials for industrialization particularly important. As the core component of sodium-ion batteries, the cathode material has a significant impact on key indicators such as battery energy density and cycle life.

[0003] The three main cathode materials for sodium-ion batteries are layered oxides, Prussian blue (white) compounds, and polyanionic compounds. Layered oxides are relatively sensitive to air, and irreversible phase transitions occur during chemical reactions, severely impacting the battery's cycle stability. The coordinated water in the Prussian blue (white) lattice is difficult to remove completely, significantly affecting the battery's capacity and cycle performance. Polyanionic compounds, on the other hand, have attracted widespread attention due to their advantages such as high operating voltage, good thermal stability, and good cycle life. In particular, the iron-based polyanionic cathode material Na4Fe3(PO4)2(P2O7) (hereinafter referred to as NFPP) combines the advantages of (PO4)... 3- The stable framework structure and (P2O7) 4- The high operating potential resulting from the induction effect, along with the ability to achieve three-electron transfer, gives it advantages such as long cycle life, high operating voltage, and high theoretical specific capacity, making it a promising candidate for large-scale energy storage applications.

[0004] The preparation methods for iron-based polyanionic cathode materials (NFPP) include high-temperature solid-state method, carbothermal reduction method, sol-gel method, hydrothermal synthesis method, and liquid-phase coprecipitation method. Among these, the high-temperature solid-state method is one of the most common and mature methods. Using ferrous iron as the main iron source, sodium and phosphorus sources are added, and after thorough grinding, sintering is performed. To prevent Fe... 2+ Oxidized into Fe 3+ During sintering, inert gas is continuously introduced, and a small amount of hydrogen is added as a reducing gas. After cooling in the furnace, NFPP is obtained. The high-temperature solid-state synthesis of NFPP has advantages such as simple process and suitability for industrialization. However, the current preparation process of NFPP is relatively complex, and the electrochemical performance of NFPP needs to be improved.

[0005] Patent application CN118263419A discloses an iron-based polyanionic sodium-ion battery cathode material with Ti3C2 nanosheets and carbon bilayer coating and its preparation method. The two-dimensional Ti3C2 nanosheets are coated twice and sintered to form Na4Fe3(PO4)2P2O7@C / Ti3C2. This can improve the electronic conductivity of the material and effectively prevent the material from agglomerating during drying and sintering, accelerate ion transport, and obtain sodium iron phosphate pyrophosphate cathode material with better performance.

[0006] Patent application CN118083938A discloses a method for preparing sodium iron pyrophosphate with flexible adjustment of compaction and electrical properties. It uses two different iron sources and a multi-stage sand milling followed by spray drying process, which shortens the sand milling time, reduces production energy consumption, and achieves a comprehensive improvement in the compaction density and electrical properties of sodium iron pyrophosphate.

[0007] However, sodium-ion batteries using NFPP as the cathode material still need improvement in terms of energy density, rate performance, and cycle life, and large-scale production and widespread application of NFPP cannot yet be achieved. Summary of the Invention

[0008] This invention addresses the aforementioned technical problems in the prior art by providing a method for preparing composite iron-based polyanionic cathode materials, the method comprising the following steps:

[0009] (1) Sodium source, ferrous source, phosphorus source, carbon source and MXenes are added to solvent water and dispersed evenly to obtain a slurry. Sodium source, ferrous source and phosphorus source are the basic raw materials for synthesizing materials, and carbon source and MXenes are the raw materials for composite coating.

[0010] (2) Place the mixed slurry in a sand mill and grind it thoroughly until the output particle size D is achieved. 50 Controlled between 200-400nm;

[0011] (3) Transfer the ground slurry into a spray dryer and spray granulate it to obtain precursor powder;

[0012] (4) The precursor powder is sintered in an inert atmosphere to obtain the composite iron-based polyanion cathode material.

[0013] The carbon source mentioned in step (1) includes iron-nickel doped polyethylene glycol, which is prepared by the following method:

[0014] K1: Mix 0.5-2 parts of ferric nitrate, 7-12 parts of 2,5-dimercaptoterephthalic acid and 300-400 parts of ethanol, heat to 40-50℃ and react for 100-150 minutes.

[0015] K2: Add 0.05-0.5 parts allyl (cyclopentadienyl) nickel and 2-6 parts sodium ethoxide, heat to 60-70℃, and react for 60-120 minutes;

[0016] K3: Add 50-70 parts of allyl polyethylene glycol, react at 60-70℃ for 100-150 minutes, and remove the ethanol by distillation after the reaction to obtain the iron-nickel doped polyethylene glycol.

[0017] Preferably, the sodium source in step (1) is one or more of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and sodium oxalate.

[0018] Preferably, the ferrous source in step (1) is one or more of ferrous phosphate octahydrate, ferrous oxalate dihydrate, ferrous pyrophosphate, and ferrous acetate.

[0019] Preferably, the phosphorus source in step (1) is one or more of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, ferrous phosphate octahydrate, and ferrous pyrophosphate.

[0020] Preferably, in step (1), MXenes is a transition metal carbonitride, which is one or more of Ti3C2, Ti3CN, Nb2C, Mo2C2 and V3C2, and is preferably Ti3CN.

[0021] Preferably, in step (1), the molar ratio of sodium in the sodium source, ferrous element in the ferrous source, and phosphorus in the phosphorus source is 4:3:4, the iron-nickel doped polyethylene glycol in the carbon source accounts for 1% of the total weight of the slurry, and the MXenes account for 0.5%-1% of the total weight of the slurry.

[0022] Preferably, the carbon source in step (1) further includes one or more of glucose, sucrose, citric acid and ascorbic acid, and the carbon source other than the iron-nickel doped polyethylene glycol accounts for 2%-4% of the total weight of the slurry.

[0023] Preferably, the mill speed in step (2) is 1500-2500 r / min, and the grinding time is 75-190 min.

[0024] Preferably, the spray drying process parameters in step (3) are as follows:

[0025] The feed rate is 55-70 mL / min, the inlet temperature is 170-210℃, and the outlet temperature is 95-105℃.

[0026] Preferably, in step (4), the sintering method is to first heat to 350℃ and hold for 4-6 hours, then heat to 500℃ and hold for 10-12 hours. The sintering temperature should not exceed 530℃, otherwise impurities will be produced, causing a decrease in electrical properties; the sintering temperature should not be lower than 480℃, otherwise the crystallinity of the material will deteriorate.

[0027] Preferably, the molecular weight of the allyl polyethylene glycol in step K3 is 1000-5000 Da, and more preferably 1000 Da, 2000 Da, 3400 Da and 5000 Da.

[0028] The present invention also provides a composite iron-based polyanionic cathode material prepared by the above method, which is sodium iron phosphate pyrophosphate composite coated with MXenes material and carbonaceous precursor, and its structural formula is expressed as Na4Fe3(PO4)2(P2O7)@C&MXenes.

[0029] The present invention also provides a sodium-ion battery, comprising a positive electrode material, an electrolyte, a negative electrode material and a separator, wherein the positive electrode material is the aforementioned composite iron-based polyanionic positive electrode material.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) This invention improves the electrochemical activity and stability of NFPP by doping polyethylene glycol, which plays a dispersing role, with iron-nickel doping: After introducing tris(2,5-dimercapto-iron(III) terephthalate and allyl(cyclopentadienyl)nickel, the introduced -OH / -COOH functional groups can provide more bonding sites for the cathode precursor, and generate a reducing atmosphere through pyrolysis during sintering, which is beneficial to the synthesis of polyanionic materials and the formation of a uniform carbon coating. The resulting composite material has excellent electrochemical performance, structural stability and thermal stability. When used as a cathode material in sodium-ion batteries, this composite material not only improves the energy density and power density of the battery, but also enhances the cycle life and safety of the battery.

[0032] (2) The sand milling combined with spray drying process used in this invention can ensure uniform dispersion of raw materials and improve the purity of sintered materials. XRD test results show that the NFPP prepared by this high-temperature solid-state method is a typical orthorhombic crystal system with space group Pn21a. In the voltage range of 2-4V, the discharge specific capacity at 0.1C can reach as high as 102mAh / g. After 50 charge-discharge cycles at 1C rate, the discharge specific capacity still remains at 90mAh / g, and the coulombic efficiency is stable at 99.9%. Its excellent cycle stability makes it suitable for large-scale energy storage applications.

[0033] (3) The chemical ratio of sodium, iron and phosphorus in the raw materials used in this invention is easy to control through ingredient mixing, and the raw materials are simple and readily available; the process used in this invention is simple, reliable, fast and easy to industrialize.

[0034] (4) The composite coating technology used in this invention coats MXenes material onto the surface of the material through in-situ pyrolysis. On the one hand, the excellent conductivity of MXenes material is used to improve the electronic conductivity of the cathode material, thereby improving the rate performance and cycle performance of the material. On the other hand, the special layered structure of MXenes material is used to improve the ion transport rate on the surface of the material, which can avoid the problem of sodium ion transport rate decreasing due to excessive coating of the conductive layer. Attached Figure Description

[0035] Figure 1 is a scanning electron microscope image of the NFPP prepared in Example 1 of the present invention.

[0036] Figure 2 is the XRD pattern of the NFPP prepared in Example 1 of the present invention.

[0037] Figure 3 is a rate charge-discharge curve of the sodium-ion battery prepared in Example 1 of the present invention.

[0038] Figure 4 is a rate charge-discharge curve of the sodium-ion battery prepared in Example 2 of the present invention.

[0039] Figure 5 is a rate charge-discharge curve of the sodium-ion battery prepared in Example 3 of the present invention.

[0040] Figure 6 is a rate charge-discharge curve of the sodium-ion battery prepared in Example 4 of the present invention.

[0041] Figure 7 shows the charge-discharge curves of the sodium-ion battery prepared in Comparative Example 1 of this invention.

[0042] Figure 8 is a cycle curve of the sodium-ion battery prepared in Example 1 of the present invention at a 1C rate. Detailed Implementation

[0043] Example 1

[0044] A method for preparing a positive electrode active material for sodium-ion batteries includes the following steps:

[0045] (1) Weigh 1 mol of sodium pyrophosphate, 1 mol of ferrous phosphate octahydrate, 1% of the total weight of iron-nickel-doped polyethylene glycol, 3% of the total weight of citric acid, and 0.5% of the total weight of Ti3CN and add them sequentially to deionized water for dispersion. Among them, sodium pyrophosphate is both a sodium source and a phosphorus source, ferrous phosphate octahydrate is both an iron source and a phosphorus source, and citric acid and Ti3CN are carbonaceous precursors;

[0046] (2) Place the mixed slurry in a sand mill and grind it at 1500 r / min for 10 min and then at 2500 r / min for 3 h. Use a particle size analyzer to check the particle size of the slurry. Once the expected particle size is reached, the precursor slurry is discharged.

[0047] (3) The precursor slurry is fed into the container. The spray dryer is set to an inlet temperature of 170℃ and an outlet temperature of 95-105℃. The feed rate is 55mL / min. The fan and heater are turned on in sequence. After the set temperature is reached, the sprayer is turned on. The slurry is continuously stirred during the feeding process until the slurry is completely sprayed. The precursor powder is then collected.

[0048] (4) The precursor powder obtained by spray drying was placed in a nitrogen atmosphere and heated to 350℃ at a heating rate of 2℃ / min and held for 4h. Then it was heated to 500℃ at a heating rate of 2℃ / min and held for 10h to obtain Na4Fe3(PO4)2(P2O7)@C&MXenes.

[0049] The preparation method of iron-nickel doped polyethylene glycol in step (1) is as follows:

[0050] K1: Mix 0.5g ferric nitrate, 7g 2,5-dimercaptoterephthalic acid and 300g ethanol, heat to 40℃ and react for 100 minutes.

[0051] K2: Add 0.05g allyl (cyclopentadienyl) nickel and 2g sodium ethoxide, heat to 60℃, and react for 60 minutes;

[0052] K3: Add 50g of allyl polyethylene glycol (molecular weight of allyl polyethylene glycol: 1000Da), react at 60℃ for 100 minutes, and after the reaction is completed, distill to remove the ethanol to obtain iron-nickel doped polyethylene glycol.

[0053] Example 2

[0054] A method for preparing a positive electrode active material for sodium-ion batteries includes the following steps:

[0055] (1) Weigh 1 mol of sodium pyrophosphate, 3 mol of ferrous oxalate dihydrate, 2 mol of ammonium dihydrogen phosphate, 1% of the total weight of iron-nickel-doped polyethylene glycol, 4% of the total weight ...

[0056] (2) Place the mixed slurry in a sand mill and grind it at 1500 r / min for 15 min, then at 2500 r / min for 2.5 h. Use a particle size analyzer to check the particle size of the slurry. Once the expected particle size is reached, discharge the precursor slurry.

[0057] (3) The precursor slurry is fed into the container. The spray dryer is set to an inlet temperature of 210℃ and an outlet temperature of 95-105℃. The feed rate is 70mL / min. The fan and heater are turned on in sequence. After the set temperature is reached, the sprayer is turned on. The slurry is continuously stirred during the feeding process until the slurry is completely sprayed. The precursor powder is then collected.

[0058] (4) The precursor powder obtained by spray drying was placed in a nitrogen atmosphere and heated to 350℃ at a heating rate of 2℃ / min and held for 6h. Then it was heated to 500℃ at a heating rate of 2℃ / min and held for 12h to obtain Na4Fe3(PO4)2(P2O7)@C&MXenes.

[0059] The preparation method of iron-nickel doped polyethylene glycol in step (1) is as follows:

[0060] K1: Mix 0.9g ferric nitrate, 9g 2,5-dimercaptoterephthalic acid and 330g ethanol, heat to 42℃ and react for 120 minutes.

[0061] K2: Add 0.1g allyl (cyclopentadienyl) nickel and 3g sodium ethoxide, heat to 62℃, and react for 80 minutes;

[0062] K3: Add 55g of allyl polyethylene glycol (molecular weight of allyl polyethylene glycol: 2000 Da), react at 62℃ for 120 minutes, and after the reaction is completed, distill to remove ethanol to obtain iron-nickel doped polyethylene glycol.

[0063] Example 3

[0064] A method for preparing a positive electrode active material for sodium-ion batteries includes the following steps:

[0065] (1) Weigh 1 mol of sodium pyrophosphate, 3 mol of ferrous acetate, 2 mol of ammonium dihydrogen phosphate, 1% of the total weight of iron-nickel-doped polyethylene glycol, 2% of the total weight of ascorbic acid, and 1% of the total weight of Mo2C2, and add them sequentially to deionized water for dispersion. Among them, sodium pyrophosphate is both a sodium source and a phosphorus source, ferrous acetate is an iron source, ammonium dihydrogen phosphate is a phosphorus source, and ascorbic acid and Mo2C2 are carbonaceous precursors;

[0066] (2) Place the mixed slurry in a sand mill and grind it at 1500 r / min for 15 min, then at 2200 r / min for 1 h. Use a particle size analyzer to check the particle size of the slurry. Once the expected particle size is reached, the precursor slurry is discharged.

[0067] (3) The precursor slurry is fed into the container. The spray dryer is set to an inlet temperature of 180℃ and an outlet temperature of 95-105℃. The feed rate is 55mL / min. The fan and heater are turned on in sequence. After the set temperature is reached, the sprayer is turned on. The slurry is continuously stirred during the feeding process until the slurry is completely sprayed. The precursor powder is then collected.

[0068] (4) The precursor powder obtained by spray drying was placed in a nitrogen atmosphere and heated to 350℃ at a heating rate of 2℃ / min and held for 6h. Then it was heated to 500℃ at a heating rate of 2℃ / min and held for 10h to obtain Na4Fe3(PO4)2(P2O7)@C&MXenes.

[0069] The preparation method of iron-nickel doped polyethylene glycol in step (1) is as follows:

[0070] K1: Mix 1g of ferric nitrate, 10g of 2,5-dimercaptoterephthalic acid and 370g of ethanol, heat to 48℃ and react for 140 minutes.

[0071] K2: Add 0.4g allyl (cyclopentadienyl) nickel and 5g sodium ethoxide, heat to 68℃, and react for 100 minutes;

[0072] K3: Add 67g of allyl polyethylene glycol (molecular weight of allyl polyethylene glycol: 3400 Da), react at 66℃ for 130 minutes, and after the reaction is completed, distill to remove ethanol to obtain iron-nickel doped polyethylene glycol.

[0073] Example 4

[0074] A method for preparing a positive electrode active material for sodium-ion batteries includes the following steps:

[0075] (1) Weigh 4 mol of sodium dihydrogen phosphate, 3 mol of ferrous oxalate dihydrate, 1% of iron-nickel-doped polyethylene glycol by weight of the raw materials, 4% of sucrose by weight of the raw materials, and 1% of Mo2C2 by weight of the raw materials, and add them sequentially to deionized water for dispersion. Among them, sodium dihydrogen phosphate is both a sodium source and a phosphorus source, ferrous oxalate dihydrate is an iron source, ammonium dihydrogen phosphate is a phosphorus source, and sucrose and Mo2C2 are carbonaceous precursors.

[0076] (2) Place the mixed slurry in a sand mill and grind it at 1500 r / min for 15 min and then at 2500 r / min for 2.5 h. Use a particle size analyzer to detect the particle size of the slurry. Once the expected particle size is reached, the precursor slurry is discharged.

[0077] (3) The precursor slurry is fed into the container. The spray dryer is set with an inlet temperature of 200℃ and an outlet temperature between 95 and 105℃. The feed rate is 65 mL / min. The blower and heater are turned on in sequence. After the set temperature is reached, the sprayer is turned on. The slurry is continuously stirred during the feeding process until the slurry is completely sprayed. The precursor powder is then collected.

[0078] (4) The precursor powder obtained by spray drying was placed in a nitrogen atmosphere and heated to 350℃ at a heating rate of 2℃ / min and held for 6h. Then it was heated to 500℃ at a heating rate of 2℃ / min and held for 10h to obtain Na4Fe3(PO4)2(P2O7)@C&MXenes.

[0079] The preparation method of iron-nickel doped polyethylene glycol in step (1) is as follows:

[0080] K1: Mix 2g of ferric nitrate, 12g of 2,5-dimercaptoterephthalic acid and 400g of ethanol, heat to 50℃ and react for 150 minutes.

[0081] K2: Add 0.5g allyl (cyclopentadienyl) nickel and 6g sodium ethoxide, heat to 70℃, and react for 120 minutes;

[0082] K3: Add 70g of allyl polyethylene glycol (molecular weight of allyl polyethylene glycol: 5000Da), react at 70℃ for 150 minutes, and after the reaction is completed, distill to remove the ethanol to obtain iron-nickel doped polyethylene glycol.

[0083] Comparative Example 1

[0084] A method for preparing a positive electrode active material for sodium-ion batteries includes the following steps:

[0085] (1) Weigh 1 mol of sodium pyrophosphate, 3 mol of ferrous oxalate dihydrate, 2 mol of ammonium dihydrogen phosphate, 1% of polyethylene glycol by weight of the raw materials, 4% of sucrose by weight of the raw materials, and 0.5% of Ti3CN by weight of the raw materials, and add them sequentially to deionized water for dispersion. Among them, sodium pyrophosphate is both a sodium source and a phosphorus source, ferrous oxalate dihydrate is an iron source, ammonium dihydrogen phosphate is a phosphorus source, and sucrose and Ti3CN are carbonaceous precursors.

[0086] (2) Place the mixed slurry in a sand mill and grind it at 1500 r / min for 15 min and then at 2500 r / min for 3 h. Use a particle size analyzer to detect the particle size of the slurry. Once the expected particle size is reached, the precursor slurry is discharged.

[0087] (3) The precursor slurry is fed into the container. The spray dryer is set with an inlet temperature of 210°C and an outlet temperature between 95°C and 105°C. The feed rate is 70 mL / min. The blower and heater are turned on in sequence. After the set temperature is reached, the sprayer is turned on. The slurry is continuously stirred during the feeding process until the slurry is completely sprayed. The precursor powder is then collected.

[0088] (4) The precursor powder obtained by spray drying was placed in a nitrogen atmosphere and heated to 350℃ at a heating rate of 2℃ / min and held for 6h. Then it was heated to 500℃ at a heating rate of 2℃ / min and held for 12h to obtain Na4Fe3(PO4)2(P2O7)@C&MXenes.

[0089] Detection Example 1

[0090] Test conditions:

[0091] The NFPP prepared in Examples 1-4 was used as the positive electrode active material for sodium-ion batteries, mixed with conductive agent SP and binder PVDF in a mass ratio of 90:5:5, with aluminum foil as the current collector to form the positive electrode; a metallic sodium sheet was used as the negative electrode for sodium ion batteries, glass fiber was used as the separator, and a 1 mol / L NaClO4 EC / DMC (volume ratio 1:1) + 5% FEC solution was used as the electrolyte. The batteries were assembled in a glove box under an argon atmosphere with an oxygen partial pressure of less than 0.01 PPM, a moisture pressure of less than 0.01 PPM, and constant current / constant voltage charge-discharge mode, with a voltage range of 2-4V, and charge-discharge tests were conducted at current densities of 0.1C-0.2C-0.5C-1C.

[0092] Figure 1 shows a scanning electron microscope (SEM) image of the NFPP prepared in Example 1 of this invention. As can be seen from the image, the particles are spherical, with a particle size of 5-45 μm and a rough surface. High-magnification images reveal relatively uniform particle morphology and the presence of distinct scaly-like structures, indicating a satisfactory composite coating effect on the particle surface.

[0093] Figure 2 shows the XRD pattern of the NFPP prepared in Example 1 of this invention. The crystal structure of the material was analyzed by X-ray diffraction. The results showed that diffraction peaks of the NFPP composite phase existed at 9.8°, 15.8°, 16.7°, 32.1°, and 33.6°, corresponding to the (200), (011), (210), (022), and (222) crystal planes of the material, respectively. The XRD results confirm that the material synthesized using this formulation and process is indeed a pure phase.

[0094] Figure 3 shows the charge-discharge curves of the sodium-ion battery prepared in Example 1 of this invention. The sample can provide discharge specific capacities of 102 mAh / g, 99 mAh / g, 97 mAh / g, and 94 mAh / g at rates of 0.1C, 0.2C, 0.5C, and 1C, respectively, with a 1C capacity retention rate of 92%.

[0095] Figure 4 shows the charge-discharge curves of the sodium-ion battery prepared in Example 2 of this invention. The sample can provide discharge specific capacities of 97 mAh / g, 95 mAh / g, 93 mAh / g, and 90 mAh / g at rates of 0.1C, 0.2C, 0.5C, and 1C, respectively, with a 1C capacity retention rate of 93%.

[0096] Figure 5 shows the charge-discharge curves of the sodium-ion battery prepared in Example 3 of this invention. The sample can provide discharge specific capacities of 81 mAh / g, 79 mAh / g, 75 mAh / g, and 70 mAh / g at rates of 0.1C, 0.2C, 0.5C, and 1C, respectively, with a 1C capacity retention rate of 86%.

[0097] Figure 6 shows the charge-discharge curves of the sodium-ion battery prepared in Example 4 of this invention. The sample can provide discharge specific capacities of 87 mAh / g, 85 mAh / g, 82 mAh / g, and 79 mAh / g at rates of 0.1C, 0.2C, 0.5C, and 1C, respectively, with a 1C capacity retention rate of 91%.

[0098] Figure 7 shows the charge-discharge curves of the sodium-ion battery prepared in Comparative Example 1 of this invention. The sample can provide discharge specific capacities of 91 mAh / g, 90 mAh / g, 88 mAh / g, and 85 mAh / g at rates of 0.1C, 0.2C, 0.5C, and 1C, respectively, with a 1C capacity retention rate of 93%.

[0099] Figure 8 shows the cycling curve of the sodium-ion battery prepared in Example 1 of this invention after 50 charge-discharge cycles at 1C. After 50 charge-discharge cycles at 1C, the discharge specific capacity still remained at 90 mAh / g, and the coulombic efficiency remained stable at 99.9%, indicating that the material has excellent cycle stability.

[0100] Compared to Example 2, Comparative Example 1 of this invention uses undoped polyethylene glycol as a dispersant. The sodium-ion battery prepared in Comparative Example 1 has a lower discharge specific capacity than that of Example 2, which shows that the doping scheme adopted in this invention can improve the electrochemical performance of NFPP.

Claims

1. A method for preparing composite iron-based polyanionic cathode materials, characterized in that, Includes the following steps: (1) Sodium source, ferrous source, phosphorus source, carbon source and MXenes are added to water and dispersed evenly to obtain a slurry. (2) Place the mixed slurry in a sand mill and grind it thoroughly until the output particle size D is achieved. 50 Controlled between 200-400nm (3) The ground slurry is transferred to a spray dryer for spray granulation to obtain precursor powder. (4) The precursor powder is sintered in an inert atmosphere to obtain the composite iron-based polyanion cathode material; The carbon source mentioned in step (1) includes iron-nickel doped polyethylene glycol, which is prepared by the following method: K1: Mix 0.5-2 parts ferric nitrate, 7-12 parts 2,5-dimercaptoterephthalic acid, and 300-400 parts ethanol, then heat to 40-50℃ and react for 100-150 minutes. K2: Add 0.05-0.5 parts allyl (cyclopentadienyl) nickel and 2-6 parts sodium ethoxide, heat to 60-70℃, and react for 60-120 minutes. K3: Add 50-70 parts of allyl polyethylene glycol, react at 60-70℃ for 100-150 minutes, and remove the ethanol by distillation after the reaction to obtain the iron-nickel doped polyethylene glycol.

2. The method for preparing composite iron-based polyanionic cathode material according to claim 1, characterized in that, The sodium source mentioned in step (1) is one or more of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, and sodium oxalate. The ferrous source is one or more of ferrous phosphate octahydrate, ferrous oxalate dihydrate, ferrous pyrophosphate, and ferrous acetate. The phosphorus source is one or more of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, ferrous phosphate octahydrate, and ferrous pyrophosphate. The MXenes are one or more of Ti3C2, Ti3CN, Nb2C, Mo2C2, and V3C2; In step (1), the molar ratio of sodium in the sodium source, ferrous element in the ferrous source, and phosphorus in the phosphorus source is 4:3:

4. The iron-nickel doped polyethylene glycol in the carbon source accounts for 1% of the total weight of the slurry, and the MXenes account for 0.5%-1% of the total weight of the slurry.

3. The method for preparing composite iron-based polyanionic cathode material according to claim 1, characterized in that, The carbon source mentioned in step (1) also includes one or more of glucose, sucrose, citric acid and ascorbic acid; The carbon source other than the iron-nickel doped polyethylene glycol accounts for 2%-4% of the total weight of the slurry.

4. The method for preparing composite iron-based polyanionic cathode material according to claim 1, characterized in that, In step (2), the speed of the sand mill is 1500-2500 r / min, and the grinding time is 75-190 min.

5. The method for preparing composite iron-based polyanionic cathode material according to claim 1, characterized in that, The spray drying process parameters in step (3) are as follows: The feed rate is 55-70 mL / min, the inlet temperature is 170-210℃, and the outlet temperature is 95-105℃.

6. The method for preparing a composite iron-based polyanionic cathode material according to claim 1, characterized in that, In step (4), the sintering method is to first heat to 350℃ and hold for 4-6 hours, then heat to 500℃ and hold for 10-12 hours.

7. The method for preparing a composite iron-based polyanionic cathode material according to claim 1, characterized in that, The molecular weight of the allyl polyethylene glycol mentioned in step K3 is 1000-5000 Da.

8. The composite iron-based polyanionic cathode material prepared by the method according to any one of claims 1 to 7.

9. A sodium-ion battery, comprising a positive electrode material, an electrolyte, a negative electrode material, and a separator, characterized in that, The cathode material is the composite iron-based polyanionic cathode material as described in claim 8.

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