Preparation method of trithiophosphatized iron / nitrogen-doped carbon composite flower balls and application thereof in sodium ion battery negative electrode materials

Abstract

The application relates to a preparation method of a trithiophosphatized iron / nitrogen-doped carbon composite flower ball and application of the trithiophosphatized iron / nitrogen-doped carbon composite flower ball in a sodium ion battery negative electrode material, and belongs to the technical field of sodium ion batteries. The method comprises the following steps: taking prepared Prussian blue as a functional precursor, and carrying out one-step gas-phase sulfur-phosphorus treatment under an inert protective atmosphere to obtain the trithiophosphatized iron / nitrogen-doped carbon composite flower ball. Compared with a traditional FePS3 preparation method, the preparation method is simple and convenient, and the morphology is controllable; the trithiophosphatized iron / carbon composite material composed of dispersed FePS3 nanosheets can be obtained without peeling, the thickness of the FePS3 nanosheet is 10-30 nm. Benefited from the structural advantages of the composite material, when the composite material is used as a sodium ion battery negative electrode material, the trithiophosphatized iron / nitrogen-doped carbon composite flower ball exhibits relatively excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically to a method for preparing iron trisulfide phosphide / nitrogen-doped carbon composite flower balls and their application in sodium-ion battery accessory materials. Background Technology

[0002] Sodium-ion batteries, due to their advantages such as abundant sodium resources, low cost, and high safety, are considered one of the candidates for next-generation large-scale energy storage devices. The electrochemical performance of sodium-ion batteries largely depends on the choice of electrode materials. For the negative electrode side, because Na... + Sodium storage anode materials have a large ionic radius and cannot be effectively embedded in commercial lithium battery anode materials such as graphite. Therefore, there is an urgent need to develop sodium storage anode materials with high specific capacity, high rate capability and long cycle life.

[0003] Ternary metal phosphide sulfide MPS x (M = Fe, Mn, Ni, Co, etc.) has become a potential new type of anode material due to its unique two-dimensional layered structure, fully exposed surface, tunable morphology, and expandable channels. Meanwhile, MPS x The electronic tunability of these materials can induce chemical diversity and intrinsic activity, resulting in faster charge conduction properties than single phosphorus / sulfide or binary layered materials. In many MPS... x Among the materials, iron trisulfide phosphide (FePS3) has a high theoretical specific capacity (1318 mAh g). -1 ) and large interlayer spacing Considered to achieve Na + FePS3 is an ideal electrode material for rapid insertion / extraction. However, despite its high theoretical specific capacity as a sodium-ion battery anode, practical applications still face challenges such as severe volume expansion, low initial coulombic efficiency, and rapid capacity decay. Furthermore, traditional synthesis methods for FePS3 typically require harsh conditions, including high temperature, high pressure, and long reaction times. This not only increases energy consumption and cost but also poses certain safety risks, limiting the practical application of FePS3.

[0004] Existing invention patent CN111261857A discloses a FePS3 / NC composite anode material for sodium-ion batteries. The resulting composite material has a layered structure with uniformly attached carbon on the surface, effectively buffering the volume expansion of the anode material during the sodium storage reaction and promoting rapid electron / ion transfer. However, the preparation process of this composite anode material is complex and the yield is low, making it unsuitable for large-scale production. Another invention patent CN111403730A discloses a FePS3@MXene nanocomposite anode material for sodium-ion batteries and its preparation method. This material has a unique 2D / 2D hybrid structure, which can promote rapid electron / ion transfer and suppress electrode volume expansion. However, its cycle life is short, and the capacity of the electrode material begins to decay significantly after 50 cycles. In addition, its preparation process is quite cumbersome, involving etching, two solid-liquid separations, and the preparation of FePS3 crystals. Therefore, it is necessary to further design and optimize the preparation process of FePS3 to improve its sodium storage specific capacity, rate capability, and cycle performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing iron trisulfide phosphide / nitrogen-doped carbon composite flower-shaped materials and their application in sodium-ion battery accessory materials. This invention uses Prussian blue with a nano-cubic structure as a functional precursor, and through a one-step gas-phase sulfur phosphating treatment, transforms cubic blocky Prussian blue into flower-shaped iron trisulfide phosphide / nitrogen-doped carbon composite materials in situ. This material exhibits excellent electrochemical performance when used as a negative electrode in sodium-ion batteries.

[0006] The technical solution of the present invention is as follows:

[0007] For the first time, this invention provides a method for preparing iron trisulfide phosphide / nitrogen-doped carbon composite flower balls, including the following steps: (1) adding iron source and polyvinylpyrrolidone to dilute hydrochloric acid and stirring evenly to obtain solution A;

[0008] (2) Solution A was subjected to a solvothermal reaction to obtain a blue suspension B;

[0009] (3) The blue suspension B was centrifuged and washed, and then dried to obtain blue powder C;

[0010] (4) Grind the blue powder C, phosphorus source and sulfur source evenly to obtain mixed powder D;

[0011] (5) Powder D is subjected to one-step gas-phase sulfur phosphating treatment to obtain a composite flower ball of iron trisulfide phosphide / nitrogen-doped carbon composed of multiple nanosheets with a thickness of 10-30 nm.

[0012] In the above steps, the main reactions that occur are as follows: First, within a certain temperature range, the iron source decomposes under acidic conditions to produce iron ions (Fe). 3+), then Fe 3+ Reduced to ferrous ions (Fe) 2+ ), ultimately Fe 2+ The Prussian blue precursor reacts with the remaining ferricyanide ions in the solution to form a precipitate. During this process, polyvinylpyrrolidone (PVP) acts as a surfactant, and its hydrophilicity and intermolecular interactions regulate and control the size and morphology of the Prussian blue, resulting in uniform nanocubes or microcubes. Subsequently, the precursor undergoes a one-step gas-phase sulfur phosphating treatment. In this process, PPVP decomposes into nitrogen-doped carbon, while Prussian blue is reduced to metallic iron under carbothermal reduction. The phosphorus and sulfur sources sublimate at high temperature to form phosphorus (P). x S y The gas is reacted with metallic iron to obtain FePS3, thus yielding a trisulfide iron phosphide / nitrogen-doped carbon composite material. This material exhibits a flower-like morphology, with FePS3 nanosheets having a thickness of 10–30 nm. This invention uses Prussian blue with a nanocubic structure as a functional precursor and successfully prepares trisulfide iron phosphide / nitrogen-doped carbon composite flower-like structures through a one-step gas-phase sulfur phosphating process. The invention uses Prussian blue with a nanocubic structure as a functional precursor and, through a one-step sulfur phosphating thermal treatment process, under the condition of coexistence of sulfur and phosphorus sources, promotes the transformation of the Prussian blue morphology from nanocubic to flower-like nanosheet structure. The obtained FePS3 nanosheets with a thickness of 10–30 nm provide more exposed electrochemical active sites, which is beneficial for Na… + Rapid intercalation and de-intercalation between the layers accelerates reaction kinetics. The resulting flower-like structure effectively suppresses interlayer aggregation and fragmentation, enhancing structural stability. Furthermore, the dual anions in the FePS3 nanosheets possess unique electronic structure regulation capabilities, enabling asynchronous participation in electrochemical reactions, which is beneficial for buffering Na+. + The internal stress generated by repeated deintercalation / intercalation. Therefore, the material of this invention exhibits excellent electrochemical performance when used as a negative electrode in sodium-ion batteries.

[0013] Furthermore, the nitrogen-doped carbon matrix (nitrogen derived from polyvinylpyrrolidone) formed during the one-step gas-phase sulfur phosphating process of this invention not only improves the conductivity of the composite material but also effectively alleviates the volume expansion and contraction of FePS3 during the electrochemical reaction process.

[0014] This invention also reveals that reaction time, reaction temperature, sulfur source, and phosphorus source are key influencing factors in the morphological transformation of FePS3 during the above reaction process: FePS3, due to its internal crystal characteristics, readily grows along the c-axis and forms a layered structure. When cubic blocky Prussian blue undergoes gas-phase sulfur phosphating treatment at a suitable temperature, Prussian blue begins to evolve into nanosheets. With prolonged heat treatment time, the nanosheets gradually increase in number and densely cover the cubic surface until the original cubic structure disappears, ultimately forming nanospheres. When the heat treatment time is too long, the nanosheets tightly aggregate, leading to agglomeration. At lower temperatures, the Prussian blue cube cannot be completely transformed into nanospheres; at higher temperatures, the cubic structure easily collapses, forming blocky materials. When only phosphorus or sulfur sources are used, the phosphide basically maintains its cubic structure, while the sulfide shrinks and aggregates severely, neither yielding a flower-like structure. Therefore, optimization of the above key process parameters is necessary.

[0015] Preferably, in step (1), the mass ratio of the iron source to polyvinylpyrrolidone is 1:(1-40).

[0016] Preferably, in step (1), the iron source is any one of potassium ferrocyanide, potassium ferrocyanide, and sodium ferrocyanide.

[0017] Preferably, in step (1), the concentration of the dilute hydrochloric acid is 0.05 to 0.2 mol / L.

[0018] Preferably, in step (2), the temperature of the solvothermal reaction is 80-120°C and the reaction time is 10-36 h.

[0019] Preferably, in step (4), the mass ratio of blue powder C, phosphorus source and sulfur source is 1:1:(1-5).

[0020] Preferably, in step (4), the phosphorus source is any one of sodium hypophosphite and red phosphorus; the sulfur source is any one of sulfur powder, thioacetamide, and thiourea.

[0021] Preferably, in step (5), the temperature of the one-step gas phase sulfur phosphating treatment is 300-700℃, the heating rate is 1-10℃ / min, and the holding time is 1-6h; the atmosphere of the one-step gas phase sulfur phosphating is nitrogen, argon, or argon-hydrogen.

[0022] Secondly, this invention provides the application of the iron trisulfide phosphide / nitrogen-doped carbon composite flower balls obtained by the above preparation method as a negative electrode material for sodium-ion batteries.

[0023] Finally, this invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode material layer coated on the surface of the current collector. The negative electrode material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material is an iron trisulfide phosphide / nitrogen-doped carbon composite flower ball.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] (1) This invention uses Prussian blue with a nanocubic structure as a functional precursor. Through a one-step sulfur phosphating heat treatment process, under the condition that sulfur source and phosphorus source coexist, the morphology of Prussian blue is transformed from nanocubic to flower-shaped nanosheet structure. Compared with the traditional preparation method, it has the advantages of being simple, convenient and having controllable morphology.

[0026] (2) The FePS3 nanosheets with a thickness of 10–30 nm prepared by this invention can provide more exposed electrochemical active sites, which is beneficial to Na + Rapid intercalation and de-intercalation between the layers accelerates reaction kinetics. The resulting flower-like structure effectively suppresses interlayer aggregation and fragmentation, enhancing structural stability. Furthermore, the dual anions in the FePS3 nanosheets possess unique electronic structure regulation capabilities, enabling asynchronous participation in electrochemical reactions, which is beneficial for buffering Na+. + Internal stress generated by repeated de-entry / entry.

[0027] (3) The nitrogen-doped carbon matrix formed during the one-step gas phase sulfur phosphating process of the present invention not only helps to improve the conductivity of the composite material, but also effectively alleviates the volume expansion and contraction of FePS3 during the electrochemical reaction process. Attached Figure Description

[0028] Figure 1 The X-ray diffraction (XRD) pattern of the final product prepared in Example 2;

[0029] Figure 2 The image shows a scanning electron microscope (SEM) image of the Prussian blue prepared in Example 4.

[0030] Figure 3 The image shows a scanning electron microscope (SEM) image of the final product prepared in Example 9.

[0031] Figure 4 The battery cycle performance diagram is shown for the final product prepared in Example 7.

[0032] Figure 5 The image shows the battery rate performance of the final product prepared in Example 3. Detailed Implementation

[0033] To make the technical problems, technical solutions and beneficial effects of the present invention easier to understand, the present invention will be described in detail below with reference to specific embodiments, but the present invention is not limited to the following examples.

[0034] (a) Different reaction temperatures

[0035] Example 1

[0036] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0037] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0038] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0039] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0040] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:3, grind them evenly to obtain a mixed powder;

[0041] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under argon-hydrogen protection and held for 4 hours to carry out one-step gas-phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0042] Example 2

[0043] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0044] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0045] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0046] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0047] (5) Weigh out blue powder, sodium hypophosphite and thiourea in a mass ratio of 1:1:3, grind them evenly to obtain a mixed powder;

[0048] (6) The mixed powder is placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min under nitrogen protection and held for 3 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0049] Example 3

[0050] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0051] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0052] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0053] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0054] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:3, grind them evenly to obtain a mixed powder;

[0055] (6) The mixed powder is placed in a tube furnace and heated to 500°C at a heating rate of 2°C / min under nitrogen protection and held for 2 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0056] Example 4

[0057] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0058] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0059] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0060] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0061] (5) Weigh out blue powder, sodium hypophosphite and thioacetamide in a mass ratio of 1:1:3, grind them evenly to obtain a mixed powder;

[0062] (6) The mixed powder is placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection and held for 2 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0063] Example 5

[0064] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0065] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0066] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0067] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0068] (5) Weigh out blue powder, sodium hypophosphite and thioacetamide in a mass ratio of 1:1:3, grind them evenly to obtain a mixed powder;

[0069] (6) The mixed powder is placed in a tube furnace and heated to 700°C at a heating rate of 10°C / min under argon protection and held for 2 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0070] (II) Ratios of different phosphorus and sulfur sources

[0071] Example 6

[0072] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0073] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0074] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0075] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0076] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:0.5, grind them evenly to obtain a mixed powder;

[0077] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0078] Example 7

[0079] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0080] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0081] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0082] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0083] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:1, grind them evenly to obtain a mixed powder;

[0084] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0085] Example 8

[0086] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0087] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0088] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0089] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0090] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:3, grind them evenly to obtain a mixed powder;

[0091] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0092] Example 9

[0093] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0094] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0095] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0096] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0097] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:5, grind them evenly to obtain a mixed powder;

[0098] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0099] Example 10

[0100] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0101] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0102] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0103] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0104] (5) Weigh out blue powder, red phosphorus and sulfur powder in a mass ratio of 1:1:7, grind them evenly to obtain a mixed powder;

[0105] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase sulfur phosphating to obtain iron trisulfide phosphide / nitrogen-doped carbon composite flower balls.

[0106] Comparative Example 1 (No sulfur source added)

[0107] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0108] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0109] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0110] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0111] (5) Weigh out blue powder and red phosphorus in a mass ratio of 1:1, grind them evenly to obtain a mixed powder;

[0112] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase phosphating to obtain iron phosphide / nitrogen-doped carbon composite material.

[0113] Comparative Example 2 (without added phosphorus source)

[0114] (1) Measure 8.2 mL of concentrated hydrochloric acid and dilute it with a small amount of water. After stirring evenly, transfer it to a 100 mL volumetric flask, add water to the mark and shake well to obtain a dilute hydrochloric acid solution.

[0115] (2) Add 1g potassium ferrocyanide and 3g polyvinylpyrrolidone to dilute hydrochloric acid and stir until well mixed;

[0116] (3) Place the solution in (2) in a reaction vessel and react at 80°C for 12 h to obtain a blue suspension;

[0117] (4) The blue suspension was washed three times with water and ethanol alternately, and then centrifuged and dried to obtain a blue powder.

[0118] (5) Weigh blue powder and sulfur powder in a mass ratio of 1:5, grind them evenly to obtain a mixed powder;

[0119] (6) The mixed powder is placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min under nitrogen protection and held for 4 hours to carry out one-step gas phase sulfur phosphating to obtain iron sulfide / nitrogen-doped carbon composite material.

[0120] Performance testing

[0121] The composite material obtained in step (5) of the above examples and comparative examples, the conductive agent (Super P), and the binder (PVDF) were mixed in a mass ratio of 7:2:1. After grinding, an appropriate amount of N-methylpyrrolidone (NMP) was added to form a uniform slurry. The slurry was then uniformly coated onto the current collector (copper foil) using a coater. After drying at 60°C for 12 hours, the slurry was cut into electrode sheets with a diameter of 12 mm for use as working electrodes. A sodium sheet was used as the counter electrode, a glass fiber membrane as the separator, and a 1 mol / L electrolyte with NaPF6 as the solute and diethylene glycol dimethyl ether as the solvent was used to assemble the button cell. The battery assembly was carried out in an argon-filled glove box, and the operation was completed from bottom to top in the following order: positive electrode shell, electrode material, separator, electrolyte, sodium sheet, gasket, spring sheet, and negative electrode shell. After the assembled sodium-ion battery was left to stand for 24 hours, a constant current charge-discharge test was performed with a voltage window of 0.01–3 V. The electrochemical performance of the negative electrode of the sodium-ion battery was measured in a constant temperature environment of 25°C.

[0122] Table 1. Capacity retention rates of Examples 1-10 and Comparative Examples 1-2 after 200 cycles.

[0123]

[0124] As shown in Table 1, the heat treatment temperature (Examples 1-5) and the ratio of sulfur to phosphorus source (Examples 6-10) significantly affect the formation of the flower-shaped structure of the composite material and its electrochemical performance when used as a sodium-ion battery anode. Excessively high or low temperatures and sulfur-to-phosphorus source ratios are detrimental to the development of high-performance sodium-ion battery anodes. Furthermore, when phosphating (Comparative Example 1) or sulfidation (Comparative Example 2) is performed alone, the phosphide maintains a largely cubic structure, while the sulfide exhibits severe shrinkage and aggregation, making it impossible to obtain a flower-shaped structure.

[0125] Figure 1 The XRD pattern of Example 2 shows that, except for the amorphous carbon peak near 26°, the other diffraction peaks are in perfect agreement with the standard card of FePS3 (PDF#72-0812), indicating that the FePS3-carbon nanocomposite material was successfully prepared.

[0126] Figure 2 The image shows a SEM image of the Prussian blue prepared in Example 4. The image shows that the Prussian blue has a nanocubic structure with relatively uniform size and a side length of approximately 200–400 nm.

[0127] Figure 3 The image shows the SEM image of the final product prepared in Example 9, and... Figure 2The morphology is quite different. After a one-step sulfur phosphating treatment, the nanocubic Prussian blue is transformed into a flower-shaped iron trisulfide phosphide / nitrogen-doped carbon composite material assembled from nanosheets (10-30 nm thick). This structure effectively inhibits the aggregation and crushing between nanosheets and enhances the structural stability.

[0128] Figure 4 The sodium-ion battery assembled from the final product prepared in Example 7 retains a specific capacity of 427 mAh / g after 500 cycles at a current density of 1 A / g.

[0129] Figure 5 The diagram shows the rate performance of the final product prepared in Example 3. The reversible specific capacities of the sodium-ion battery at current densities of 0.2, 0.5, 1, 2, 3, 4, and 5 A / g are 416, 395, 385, 368, 334, 279, and 249 mAh / g, respectively. The specific capacity at 0.2 A / g is 372 mAh / g, and the capacity retention is 89.5%.

[0130] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing iron trisulfide phosphide / nitrogen-doped carbon composite flower balls, characterized in that, Includes the following steps: (1) Add the iron source and polyvinylpyrrolidone to dilute hydrochloric acid and stir until homogeneous to obtain solution A; the mass ratio of the iron source to polyvinylpyrrolidone is 1:(1~40); the iron source is any one of potassium ferricyanide, potassium ferrocyanide, and sodium ferrocyanide; (2) Solution A is subjected to a solvothermal reaction to obtain a blue suspension B; the temperature of the solvothermal reaction is 80~120℃ and the reaction time is 10~36 h; (3) The blue suspension B was centrifuged and washed, and then dried to obtain blue powder C; the mass ratio of blue powder C, phosphorus source and sulfur source was 1:1:(1~5). (4) Grind the blue powder C, phosphorus source and sulfur source evenly to obtain mixed powder D; (5) Powder D is subjected to one-step gas-phase sulfur phosphating treatment to obtain a composite flower ball of iron trisulfide phosphide / nitrogen-doped carbon composed of multiple nanosheets with a thickness of 10~30 nm.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the dilute hydrochloric acid is 0.05~0.2 mol / L.

3. The preparation method according to claim 1, characterized in that: In step (4), The phosphorus source is either sodium hypophosphite or red phosphorus. The sulfur source is any one of sulfur powder, thioacetamide, or thiourea.

4. The preparation method according to claim 1, characterized in that: In step (5), the temperature of the one-step gas phase sulfur phosphating treatment is 300~700 ℃, the heating rate is 1~10 ℃ / min, and the holding time is 1~6 h; The atmosphere for the one-step gas-phase sulfur phosphating is nitrogen, argon, or argon-hydrogen.

5. The application of the iron trisulfide phosphide / nitrogen-doped carbon composite flower ball obtained by the preparation method according to any one of claims 1 to 4 as a negative electrode material for sodium-ion batteries.

6. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode material layer coated on the surface of the current collector, the negative electrode material layer comprising a negative electrode active material, a conductive agent, and a binder, characterized in that: The negative electrode active material is the iron trisulfide phosphide / nitrogen-doped carbon composite flower ball obtained by the preparation method described in any one of claims 1 to 4.

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