A method for directly preparing metal element-doped iron fluoride positive electrode material in aqueous solution and application

Abstract

The application relates to the field of nanomaterials and electrochemical technology, in particular to a method for directly preparing metal element doped iron fluoride positive electrode materials in an aqueous solution. The method for directly preparing metal element doped iron fluoride positive electrode materials in an aqueous solution comprises the following steps: S1, sequentially adding an iron source and a doped metal source into a hydrofluoric acid solution, adding hydrogen peroxide solution into the reaction solution until the reaction solution is colorless and transparent after the reaction is completed; S2, adding a conductive modification material into the colorless and transparent solution, stirring for a period of time to obtain a mixed solution, and sequentially carrying out freezing and drying treatment on the mixed solution to obtain an intermediate product; and S3, placing the intermediate product in a protective atmosphere and carrying out calcination treatment for a period of time to obtain the metal element doped iron fluoride positive electrode material.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and electrochemical technology, specifically to a method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution. Background Technology

[0002] Currently, the cost of cathode materials for commercially available lithium-ion and sodium-ion batteries accounts for more than 40% of the total cost, making the cathode materials for lithium-ion / sodium-ion batteries extremely expensive.

[0003] Unlike transition metal sulfides and oxide anode materials, transition metal fluorides, due to their unique coordination interactions between metal ions and fluoride ions, can be used as cathode materials for lithium-ion / sodium-ion batteries. Among all transition metal fluorides, iron trifluoride (Fe3F) has attracted significant attention from researchers due to its low cost, abundant iron resources, high operating voltage, and environmental friendliness. Generally, the synthesis methods for Fe3F can be divided into three types: gas-phase synthesis, solid-phase synthesis, and liquid-phase synthesis. Gas-phase synthesis involves the direct reaction of fluorine-containing gases (such as F2, NF3, and HF) with iron-containing precursors to prepare Fe3F. These gases are typically highly toxic and pose significant production safety risks. Solid-phase synthesis involves reacting an iron-source precursor with a fluorine source (such as NH4F, polytetrafluoroethylene, and CF3F). x Ferrofrium fluoride is prepared by direct sintering at high temperatures. High-energy ball milling is often used to reduce the particle size of the electrode material and improve its electrochemical performance. However, this method often consumes a large amount of energy, contradicting the initial goal of low-cost sodium-ion batteries. Liquid-phase synthesis offers advantages such as better control of reaction parameters and the ability to produce materials with controllable morphology and properties. However, because ferrofluoride is readily soluble in water, the yield of precipitated ferrofluoride crystals during solvothermal methods is low. Therefore, the direct use of water as a solvent is usually avoided; instead, organic solvents or ionic liquids are used to improve the yield.

[0004] Over the past decade, it has been discovered that, unlike the dense structure of FeF3, the open ion channels in FeF3 hydrates facilitate ion diffusion and improve inherent conductivity, which helps enhance the reversible capacity and rate performance of FeF3 materials. Based on this, researchers have investigated various FeF3 hydrates, such as hexagonal tungsten bronze (FeF3·0.33H2O), tantalite (FeF3·0.5H2O), and the cubic ore Fe2F5·H2O. However, these synthetic methods use ionic liquids as solvents to synthesize FeF3 hydrates, resulting in high costs. Furthermore, researchers have found that doping FeF3 or FeF3 hydrates with cations (such as Mn, Ni, Co, Ti, Cu, etc.) can improve battery cycle life and mitigate capacity decay. However, the synthesis steps involve solid-phase high-energy ball milling, gas-phase fluorination, and the preparation of a co-precipitated precursor of hydroxides in the liquid phase, or a combination of both, accompanied by a high-temperature sintering process (>500℃). This process is lengthy and energy-intensive, contradicting the initial goal of low-cost sodium-ion batteries. Therefore, the present invention aims to provide a method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution. Summary of the Invention

[0005] This invention provides a method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution.

[0006] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0007] S1. Add the iron source and the doped metal source to the hydrofluoric acid solution in sequence. After the reaction is completed, add hydrogen peroxide solution dropwise to the reaction solution until the reaction solution becomes colorless and transparent.

[0008] S2. Add conductive modifying material to a colorless and transparent solution, stir for a period of time to obtain a mixed solution, and then freeze and dry the mixed solution in sequence to obtain an intermediate product.

[0009] S3. After calcining the intermediate product in a protective atmosphere for a period of time, metal element-doped iron fluoride cathode material is obtained.

[0010] Furthermore, in S1, the concentration of hydrofluoric acid is 5–22.8 mol / L, and the stoichiometric ratio of iron source to doped metal source is 100:0–50.

[0011] Furthermore, the iron source is elemental iron or iron oxide, and the doping metal source is elemental metal or metal oxide.

[0012] Furthermore, in S1, the concentration of hydrogen peroxide solution is 3–9.9 mol / L.

[0013] Furthermore, in S2, the conductive modification material is one of graphene oxide, graphene, carbon nanotubes, conductive carbon black, porous carbon, and graphite.

[0014] Furthermore, in S2, the conductive modifier accounts for 0-50% of the mass of the product.

[0015] Furthermore, in S2, the freeze-drying temperature conditions are -20 to -200°C, and the time conditions are 1 to 5 days.

[0016] Furthermore, in S3, the calcination temperature is 180℃-250℃ and the time is 1-48h.

[0017] The above method yields a metal element-doped iron fluoride cathode material.

[0018] The above-mentioned metal-doped iron fluoride cathode material is used in the preparation of sodium-ion batteries.

[0019] The beneficial effects of this invention are as follows: The method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution according to this invention results in the formation of stable and easily soluble ionic clusters, FeF6, during the preparation process. 3- Therefore, in the subsequent freezing process, the atomic-level uniform composite of doping elements and iron elements can be achieved. At the same time, the product will also nucleate and grow in situ on the conductive material substrate, constructing an excellent conductive network in situ. The final metal element-doped iron fluoride cathode material has excellent cycle performance and rate performance.

[0020] Furthermore, the preparation method of this invention does not require the addition of any water solvent (the amount of water used is extremely small), and only a small amount of water is sublimated during the freezing process. There is no emission of other pollutants (F2, NF3, etc.) or introduction of auxiliary chemical reagents (such as NaOH, etc.). At the same time, there is no high-temperature sintering process, and iron, fluorine and doping elements are ultimately used to form iron fluoride cathode material, which meets environmental protection requirements. Attached Figure Description

[0021] Figure 1 This is an experimental flowchart of a method for directly preparing metal element-doped iron fluoride cathode material in aqueous solution according to the present invention.

[0022] Figure 2 This is a schematic diagram illustrating the dissolution mechanism of hydrogen peroxide solution added to a mixture of iron source and doped metal source according to the present invention;

[0023] Figure 3 This is the XRD diffraction pattern of the precipitated crystal (Na3FeF6) obtained in Example 1 of this invention;

[0024] Figure 4ab are both Sn in Embodiment 2 of the present invention. 0.08 Fe 0.92 Electron micrograph of F3·0.33H2O / GO;

[0025] Figure 5 This is a cycle performance diagram of the Sn-doped iron fluoride cathode material prepared in Examples 1, 2 and 3 of this invention in a sodium-ion half-cell at a current density of 20 mA / g.

[0026] Figure 6 These are color change comparison diagrams during the preparation process of the metal element-doped iron fluoride cathode materials obtained in Examples 1, 2, 3, and 4 of this invention.

[0027] Figure 7 These are the XRD diffraction patterns of the metal element-doped iron fluoride cathode materials prepared in Examples 1, 3, and 4 of this invention. Detailed Implementation

[0028] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0029] like Figure 1-2 As shown, a method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0030] S1. Transfer hydrofluoric acid of a certain concentration into a reaction vessel while stirring slowly.

[0031] S2. Slowly add the iron source and the doped metal source to the hydrofluoric acid solution. After the reaction is complete, add a certain concentration of hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless and transparent. The stoichiometric ratio of the iron source and the doped metal source is between 100:0 and 50. The iron source is iron powder (Fe) or iron oxide (such as one of FeO, Fe2O3, or Fe4O3), and the doped metal source is a single elemental metal (Me) or a metal oxide (Me2). or 1O x It should be noted that this step utilizes the strong oxidizing properties of H2O2 to completely dissolve the Fe, forming a colorless, transparent, and highly stable FeF6. 3- .

[0032] S3. Add a certain amount of conductive modification material to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution. The conductive modification material is one of graphene oxide, graphene, carbon nanotubes, conductive carbon black, porous carbon, and graphite. It should be noted that this step is completed in a fume hood.

[0033] S4. Transfer the mixed solution obtained in S3 to a low-temperature (-200℃-10℃) freezing device, freeze for 1 to 5 days, and then perform vacuum freeze-drying to obtain the intermediate product.

[0034] S5. The intermediate product obtained in S4 is placed in a tube furnace under an inert atmosphere (including but not limited to Ar, N2) (40cc / min) and baked at a temperature of 180℃-250℃ for 1 to 48 hours to obtain the metal element-doped iron fluoride cathode material.

[0035] This invention discloses a method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution, which utilizes the formation of stable and easily soluble ionic clusters, FeF6, during the preparation process. 3- Therefore, in the subsequent freezing process, the atomic-level uniform composite of doping elements and iron elements can be achieved. At the same time, the product will also nucleate and grow in situ on the conductive material substrate, constructing an excellent conductive network in situ. The final metal element-doped iron fluoride cathode material has excellent cycle performance and rate performance.

[0036] Furthermore, the preparation method of this invention does not require the addition of any water solvent (the amount of water used is extremely small), and only a small amount of water is sublimated during the freezing process. There is no emission of other pollutants (F2, NF3, etc.) or introduction of auxiliary chemical reagents (such as NaOH, etc.). At the same time, there is no high-temperature junction process above 500°C. Iron, fluorine and doping elements are all ultimately used to generate iron fluoride cathode material, which meets environmental protection requirements.

[0037] <Example 1>

[0038] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0039] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0040] S2. Slowly add 1.00g of iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5mL of 9.9mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0041] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0042] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0043] S5. The intermediate product obtained in S4 is placed in a tube furnace with an Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material FeF3·0.33H2O / GO. It is abbreviated as Fe or SnO.

[0044] To verify that the formation of S2 yielded colorless, transparent, and highly stable FeF6. 3- Adding saturated sodium chloride solution to the colorless solution obtained in S2 resulted in the precipitation of a white precipitate. XRD analysis of this white precipitate revealed it to be Na3FeF6 crystals; the results are shown below. Figure 3 This proves that the addition of H2O2 forms colorless, transparent, and highly stable FeF6. 3- Complex ion group.

[0045] <Example 2>

[0046] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0047] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0048] S2. Slowly add iron powder (Fe) and tin powder (Sn) to the hydrofluoric acid solution. After the reaction is complete, add 5 mL of 9.9 mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless. The stoichiometry of iron and tin is 92:8.

[0049] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0050] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0051] S5. The intermediate product obtained in S4 is placed in a tube furnace with an Ar gas flow (40cc / min) and baked at 220°C for 6 hours to obtain a metal element-doped iron fluoride cathode material, denoted as Sn. 0.08 Fe 0.92 F3·0.33H2O / GO, abbreviated as Sn8.

[0052] Sn obtained in this embodiment 0.08 Fe 0.92 The electron micrograph of F3·0.33H2O / GO is shown in the figure below. Figure 4 As shown, by Figure 4 It is known that Sn with a diameter of approximately 500 nm in the nanometer size... 0.08 Fe 0.92 Spherical particles of F3·0.33H2O are uniformly dispersed in a thin layer of graphene, forming a Sn network with good conductive pathways. 0.08 Fe 0.92 F3·0.33H2O / GO nanocomposite material.

[0053] To further explore the optimal Sn doping ratio in Example 2, the Fe:Sn stoichiometric ratio in step S2 of Example 2 was extended to different ranges: 94:6, 96:4, or 50:50. Step S5 can be sequentially denoted as Sn. 0.06 Fe 0.94 F3·0.33H2O / GO, or Sn 0.04 Fe 0.96 F3·0.33H2O / GO, or Sn 0.5 Fe 0.5 F3·0.33H2O / GO can be abbreviated as Sn6, Sn4, or Sn50, respectively.

[0054] <Example 3>

[0055] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0056] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0057] S2. Slowly add iron powder (Fe) and tin powder (Sn) to the hydrofluoric acid solution. After the reaction is complete, add 5 mL of 9.9 mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless. The stoichiometry of iron and tin is 90:10.

[0058] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0059] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0060] S5. The intermediate product obtained in S4 is placed in a tube furnace with an Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material Sn. 0.1 Fe 0.9F3·0.33H2O / GO, abbreviated as Sn10.

[0061] The performance of sodium-ion half-cells assembled from some of the materials in Implementation Cases 1, 2, and 3 is shown in Table 1.

[0062]

[0063] Table 1: Cyclic performance of Sn-doped (Sn10, Sn8, Sn6, Sn4)FeF3·0.33H2O materials and undoped Sn FeF3·0.33H2O (Sn0) materials in sodium-ion half-cells at a current of 20 mA / g.

[0064] As shown in Table 1, the appropriate control of Sn doping amount has a very important impact on the electrochemical performance of the final material. Among them, Sn8 obtained with an 8% doping ratio has the best comprehensive performance in terms of electrochemical capacity, cycling performance and capacity retention.

[0065] Figure 5 This figure shows the cycling performance of the partially Sn-doped iron fluoride cathode materials prepared in Examples 1, 2, and 3 of this invention in a sodium-ion half-cell at a current density of 20 mA / g. The figure clearly shows that the Sn doping ratio has a significant impact on the material's performance in the sodium-ion battery. As the Sn doping content increases, the electrochemical cycling stability gradually improves, but the actual reversible cycle capacity gradually decreases. At a Sn doping content of approximately 8%, the cycling stability and actual reversible cycle capacity reach an optimal balance. Therefore, a reasonable doping amount of heterogeneous elements can improve the electrochemical performance.

[0066] To further explore the scalability of other metal doping methods in Example 3, the iron powder (Fe) and tin powder (Sn) in step S2 of Example 3 were replaced with iron powder (Fe) and nickel powder (Ni), or iron powder (Fe) and titanium powder (Ti). Step S5 can then be sequentially denoted as Ni... 0.1 Fe 0.9 F3·0.33H2O / GO, or Ti 0.1 Fe 0.9 F3·0.33H2O / GO can be abbreviated as Ni10 or Ti10.

[0067] <Example 4>

[0068] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0069] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0070] S2. Slowly add iron powder (Fe) and zinc oxide powder (ZnO) to the hydrofluoric acid solution. After the reaction is complete, add 5 mL of 9.9 mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless. The stoichiometry of iron and zinc is 90:10.

[0071] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0072] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0073] S5. The intermediate product obtained in S4 is placed in a tube furnace with an Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material Zn. 0.1 Fe 0.92 F3·0.33H2O / GO, abbreviated as Zn10.

[0074] Figure 7 The XRD diffraction patterns of some products obtained in Examples 1, 3, and 4 show that the diffraction peak positions are basically consistent with those of the standard FeF3·0.33H2O card, with no impurity diffraction peaks appearing. This indicates that heteroatoms have been doped into the bulk lattice without forming new impurity phases. This further demonstrates the high scalability of this method for metal doping, allowing for the easy and controllable doping of various metal elements during the preparation of FeF3·0.33H2O materials.

[0075] <Example 6>

[0076] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0077] S1. Transfer 45 mL of 5 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0078] S2. Slowly add iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5 mL of 9.9 mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0079] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0080] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0081] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the iron fluoride cathode material FeF3·0.33H2O / GO.

[0082] <Example 7>

[0083] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0084] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0085] S2. Slowly add iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 17 mL of 3 mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0086] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0087] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0088] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the iron fluoride cathode material FeF3·0.33H2O / GO.

[0089] <Example 8>

[0090] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0091] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0092] S2. Slowly add 1.00g of iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5mL of 9.9mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0093] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0094] S4. The mixed solution obtained in S3 is instantaneously freeze-dried with liquid nitrogen at a temperature of -200℃, and then transferred to a refrigeration device for 24 hours of vacuum freeze-drying to obtain an intermediate product.

[0095] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material FeF3·0.33H2O / GO.

[0096] <Example 9>

[0097] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0098] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0099] S2. Slowly add 1.00g of iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5mL of 9.9mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0100] S3. Add 0.2g of multi-walled carbon nanotubes to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0101] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0102] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material FeF3·0.33H2O / CNT.

[0103] <Example 10>

[0104] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0105] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0106] S2. Slowly add 1.00g of iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5mL of 9.9mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0107] S3. Add 1g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0108] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0109] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 220℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material FeF3·0.33H2O / GO.

[0110] <Example 11>

[0111] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0112] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0113] S2. Slowly add 1.00g of iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5mL of 9.9mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0114] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0115] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0116] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 180℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material FeF3·0.33H2O / GO.

[0117] <Example 12>

[0118] A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution includes the following steps:

[0119] S1. Transfer 10 mL of 22.8 mol / L hydrofluoric acid to the reaction vessel while stirring slowly.

[0120] S2. Slowly add 1.00g of iron powder (Fe) to the hydrofluoric acid solution. After the reaction is complete, add 5mL of 9.9mol / L hydrogen peroxide solution dropwise to the reaction solution until the reaction solution is colorless.

[0121] S3. Add 0.2g of graphene oxide to the colorless and transparent solution of S2 and stir for 30 minutes to obtain a dark gray mixed solution.

[0122] S4. Transfer the mixed solution obtained in S3 to a freezing device, freeze it at -60℃ for 2 hours, and then perform vacuum freeze-drying for 24 hours to obtain the intermediate product.

[0123] S5. The intermediate product obtained in S4 is placed in a tube furnace with Ar gas flow (40cc / min) and baked at 250℃ for 6 hours to obtain the metal element-doped iron fluoride cathode material FeF3·0.33H2O / GO.

[0124] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for directly preparing metal-doped iron fluoride cathode materials in aqueous solution, characterized in that, Includes the following steps: S1. Add the iron source and the doped metal source to the hydrofluoric acid solution in sequence. After the reaction is complete, add hydrogen peroxide solution dropwise to the reaction solution until the reaction solution becomes colorless and transparent. The concentration of hydrofluoric acid is 5~22.8 mol / L. Based on the stoichiometric ratio, the ratio of iron source to doped metal source is 100:0.08~50. S2. Add a conductive modifier to a colorless and transparent solution, stir for a period of time to obtain a mixed solution, and then freeze and dry the mixed solution in sequence to obtain an intermediate product; the conductive modifier is one of graphene oxide, graphene, carbon nanotubes, conductive carbon black, porous carbon, and graphite. S3. After calcining the intermediate product in a protective atmosphere for a period of time, the calcination temperature is 180℃-250℃ and the time is 1~48 h, to obtain the metal element-doped iron fluoride cathode material.

2. The method for directly preparing metal-doped iron fluoride cathode material in aqueous solution according to claim 1, characterized in that, The iron source is elemental iron or iron oxide, and the doping metal source is elemental metal or metal oxide.

3. The method for directly preparing metal-doped iron fluoride cathode material in aqueous solution according to claim 1, characterized in that, In S1, the concentration of hydrogen peroxide solution is 3~9.9 mol / L.

4. The method for directly preparing metal-doped iron fluoride cathode material in aqueous solution according to claim 1, characterized in that, In S2, the conductive modification material accounts for 2.5% to 50% of the mass of the intermediate product.

5. The method for directly preparing metal-doped iron fluoride cathode material in aqueous solution according to claim 1, characterized in that, In S2, the freeze-drying temperature conditions are -10 ~ -200 ℃, and the time conditions are 1 ~ 5 days.

6. The method for directly preparing metal-doped iron fluoride cathode material in aqueous solution according to claim 1, characterized in that, In S3, the calcination temperature is 180℃-250℃ and the time is 1~48 h.

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