A Prussian blue-derived iron fluoride@carbon composite material, its preparation method and application

Abstract

This invention belongs to the field of energy storage materials technology, specifically relating to a Prussian blue-derived iron fluoride@carbon composite material, its preparation method, and its application. The preparation method includes the following steps: (1) using Prussian blue as the iron source, mixing it uniformly with a carbon source, and then heat-treating it to obtain a Fe3O4@C precursor; (2) fluorinating the Fe3O4@C precursor obtained in step (1); (3) drying the fluorinated sample in a vacuum oven at 50-90℃ to obtain an iron fluoride@C composite material containing water of crystallization; (4) heat-treating the dried sample to remove some of the water of crystallization, thus obtaining the Prussian blue-derived iron fluoride@carbon composite material. The iron source used in this invention is Prussian blue, which, during high-temperature carbonization, coats the metal compound with a nitrogen-doped carbon layer, effectively improving the material's conductivity. The material prepared by this invention exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials technology, specifically relating to a Prussian blue-derived iron fluoride@carbon composite material, its preparation method, and its application. Background Technology

[0002] Energy and environmental issues are two hot topics in the 21st century, attracting increasing attention. Batteries, as carriers of electrical energy, have become a crucial component of the energy system. Over the past few decades, lithium-ion batteries, with their advantages of high reversible capacity, high discharge voltage, and high energy density, have developed rapidly, greatly satisfying the needs of energy storage and conversion. However, with the continuous development of electric vehicles and large-scale energy storage devices, the demand for high-energy-density, high-power-density lithium-ion batteries (LIBs) is also constantly increasing. The lithium storage performance of LIBs is mainly determined by the electrode materials. With the rapid emergence and application of advanced anode materials, cathode materials have become a significant factor hindering the improvement of lithium-ion battery energy density. Traditional cathode materials have limited capacity, and most cathode materials have a discharge plateau of approximately 2-4V. Therefore, developing cathode materials with higher specific capacity, longer cycle life, and higher discharge plateaus is the future development trend.

[0003] Transition metal fluorides M x F y Metals such as Fe, Co, Ni, Cu, and Al (M = Fe, Co, Ni, Cu, Al, etc.) possess strong ionic bonds and exhibit high theoretical potentials when used as electrode materials. Furthermore, transition metal fluorides can achieve ultra-high lithium storage capacity through conversion reactions. Among these, iron fluoride has attracted widespread attention from researchers due to its advantages, including a high discharge potential (~3.4V), high capacity (712 mAh / g), low cost, non-toxicity, and environmental friendliness.

[0004] However, several issues remain to be addressed for the further commercialization of FeF3 materials (e.g., poor rate capability and cycle performance, large volume expansion during charge and discharge, and low electronic conductivity), primarily due to the strong ionic bonding characteristics of Fe-F. Researchers are attempting to improve the overall conductivity of the electrode and thus enhance its electrochemical performance by constructing composite structures. Carbon materials possess good conductivity, large specific surface area, chemical stability, and certain mechanical properties. Their application in the design of iron-based fluoride composites can effectively improve the conductivity of iron-based fluorides, alleviate their volume expansion and pulverization during conversion reactions, and improve the electrochemical reaction interface on the surface of iron-based fluorides, inhibiting side reactions and the loss of active materials. However, excessive carbon coating can hinder electrolyte transport, reducing the material's discharge capacity and negatively impacting the lithium storage performance of iron-based fluorides.

[0005] By indexing, Chinese patent CN 114551824 A was found to disclose a composite iron fluoride cathode material and its preparation method and application. The iron source used in this patent is a conventional iron salt, specifically iron nitrate, iron sulfate, iron chloride, iron oxalate, and iron acetate. Strip-shaped microspheres of FeF3·0.33H2O@C are prepared. This scheme still has the following problems: (1) The scheme requires a lot of reagents. In addition to the carbon source and iron source, there is also a two-phase mixture of sorbitan trioleate and isooctane and the presence of disodium ethylenediaminetetraacetate chelating agent, making the synthesis process complicated; (2) The iron fluoride content in the material synthesized by this scheme is low, only 39.04 wt%; (3) The material synthesized by this scheme, as a battery active material, can achieve a specific capacity of 153 mA hg during the first discharge under the conditions of a rate of 0.2C and a charge-discharge voltage range of 2.0V-4.5V. -1 After 200 cycles, the discharge specific capacity remains at 119 mA hg. -1 The energy efficiency reaches 85%, but the electrochemical performance needs to be improved. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a Prussian blue-derived iron fluoride@carbon composite material, its preparation method and application.

[0007] The technical solution adopted in this invention is as follows: A method for preparing a Prussian blue-derived iron fluoride@carbon composite material, comprising the following steps:

[0008] (1) Using Prussian blue as the iron source, it is mixed evenly with carbon source and then heat-treated to obtain Fe3O4@C precursor;

[0009] (2) Fluoride the Fe3O4@C precursor obtained in step (1);

[0010] (3) The fluorinated sample from step (2) was dried in a vacuum oven at 50-90℃ to obtain a fluorinated iron@C composite material containing water of crystallization;

[0011] (4) The dried sample was heat-treated to remove some of the water of crystallization and Prussian blue-derived iron fluoride@carbon composite material was obtained.

[0012] Preferably, in step (1), the carbon source is glucose, and the mass ratio of glucose to Prussian blue is 0.2-1.0.

[0013] Preferably, in step (1), Prussian blue and carbon source are dispersed in anhydrous ethanol, then placed in an oven at 50-70°C for 4-8 hours, and then annealed at 500-800°C for 4-8 hours under an inert gas atmosphere to obtain Fe3O4@C precursor.

[0014] Preferably, in step (2), the Fe3O4@C precursor is added to a reactor containing HF solution for hydrothermal fluorination reaction.

[0015] Preferably, in step (2), the concentration of the HF solution is 30-60 wt%, the temperature of the fluorination reaction is 90-120℃, and the time is 3-6 h.

[0016] Preferably, in step (3), the fluorinated sample in step (2) is washed and centrifuged with ethanol before drying.

[0017] Preferably, in step (4), the heat treatment temperature is 200-300℃ and the time is 6-12 h.

[0018] The Prussian blue-derived iron fluoride@carbon composite material was prepared by the method described above.

[0019] The Prussian blue-derived iron fluoride@carbon composite material, as described above, is used in the preparation of electrode materials.

[0020] The Prussian blue-derived iron fluoride@carbon composite material described above is used in the preparation of lithium batteries.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. The iron source used in this invention is Prussian blue, which differs from other methods that use iron salts as raw materials. Prussian blue (PB), as a face-centered cubic crystal structure, has a mixed valence state [Fe]. 2+ (CN)6] 4− and Fe 3+ It has a rich iron content, low cost, and controllable shape; the present invention found that during the high-temperature carbonization process, a nitrogen-doped carbon layer is coated on the outside of the metal compound, which can effectively improve the conductivity of the material.

[0023] 2. The Prussian blue-derived iron fluoride@carbon composite material prepared by this invention contains water of crystallization. By combining with carbon, the volume expansion of iron fluoride particles during charging and discharging can be suppressed, and direct contact between iron fluoride and electrolyte can be avoided. This can effectively suppress the occurrence of side reactions, thereby improving the long-cycle performance of the material. In addition, it can also improve the conductivity of the material and enhance its performance.

[0024] 3. The Prussian blue-derived iron fluoride@carbon composite material prepared by this invention possesses a unique ion tunnel, which can shorten the Li... + The longer the transmission distance and the better the rate performance, the better its electrochemical performance at high current densities. When used as the positive electrode of a lithium-ion battery, it can reach a maximum voltage of 4.2 V, effectively expanding the discharge window of the full cell and improving the energy density of the battery device.

[0025] The Prussian blue-derived iron fluoride@carbon composite material prepared in one embodiment of the present invention, at 100 mA g -1 At the current density, the discharge capacity after 100 cycles is 148.48 mAh g. -1 ; at 2000 mA g -1 At the current density, the initial discharge capacity is 135.55 mAh g. -1 After 100 cycles, the discharge capacity was 119.60 mAh g. -1 The capacity retention rate was 88.59%, which indicates that the Prussian blue-derived iron fluoride@carbon composite material prepared by this invention has excellent electrochemical performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0027] Figure 1 This is a schematic diagram of the process for the FeF3·0.33H2O@C material of the present invention;

[0028] Figure 2 The XRD pattern of FeF3·0.33H2O@C prepared in Example 1 of this invention;

[0029] Figure 3 The images show the X-ray photoelectron spectroscopy (XPS) spectra of the FeF3·0.33H2O@C material prepared in Example 1 of this invention, including: (a) XPS full spectrum scan; (b) F 1s spectrum; (c) Fe 2p spectrum; (d) C 1s spectrum; and (e) O 1s spectrum.

[0030] Figure 4 In the figures, (a) is the FeF3·0.33H2O@C material prepared in Example 1 of the present invention; (b) is the FeF3·0.33H2O material prepared in Comparative Example 1 of the present invention; and (c) is a scanning electron microscope (SEM) image of the FeF3·0.33H2O@C-2 material prepared in Comparative Example 2 of the present invention.

[0031] Figure 5 In the figures, (a) shows the FeF3·0.33H2O material prepared in Comparative Example 1 of the present invention; (b) shows the X-ray diffractometer (XRD) of the FeF3·0.33H2O@C-2 material prepared in Comparative Example 2 of the present invention.

[0032] Figure 6 Thermogravimetric analysis (TGA) curves of the FeF3·0.33H2O@C material prepared in Example 1 of the present invention, the FeF3·0.33H2O material prepared in Comparative Example 1 of the present invention, and the FeF3·0.33H2O@C-2 material prepared in Comparative Example 2 of the present invention;

[0033] Figure 7 Electrochemical performance graphs of FeF3·0.33H2O@C prepared in Example 1, FeF3·0.33H2O prepared in Comparative Example 1, and FeF3·0.33H2O@C-2 prepared in Comparative Example 2 are shown below.

[0034] (a) Batteries assembled from FeF3·0.33H2O@C, FeF3·0.33H2O, and FeF3·0.33H2O@C-2 materials were tested at 100 mA g. -1 Cyclic capacity and coulombic efficiency test curves at current density;

[0035] (b) Batteries assembled from FeF3·0.33H2O@C, FeF3·0.33H2O, and FeF3·0.33H2O@C-2 materials were tested at 1000 mA g. -1 Cyclic capacity and coulombic efficiency test curves at current density;

[0036] (c) Rate performance diagrams of batteries assembled from FeF3·0.33H2O@C, FeF3·0.33H2O, and FeF3·0.33H2O@C-2 materials respectively;

[0037] (d) Nyquist plots of batteries assembled from FeF3·0.33H2O@C, FeF3·0.33H2O, and FeF3·0.33H2O@C-2 materials, respectively;

[0038] Figure 8 The electrochemical performance diagram of FeF3·0.33H2O@C prepared in Example 1 of this invention is shown below, where:

[0039] (a) Cyclic voltammetry curves of batteries assembled with FeF3·0.33H2O@C material at different scan rates;

[0040] (b) A battery assembled with FeF3·0.33H2O@C material at 2000 mA g -1 Cyclic capacity and coulombic efficiency test curves at current density. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0042] This invention provides a method for preparing a Prussian blue-derived iron fluoride@carbon composite material, such as... Figure 1 As shown, it includes the following steps:

[0043] (1) Using Prussian blue as the iron source, it is mixed evenly with carbon source and then heat-treated to obtain Fe3O4@C precursor;

[0044] (2) Fluoride the Fe3O4@C precursor obtained in step (1);

[0045] (3) The fluorinated sample from step (2) was dried in a vacuum oven at 50-90℃ to obtain a fluorinated iron@C composite material containing water of crystallization.

[0046] (4) The dried sample was heat-treated to remove some of the water of crystallization and Prussian blue-derived iron fluoride@carbon composite material was obtained.

[0047] Prussian blue analogues (PBAs) are a class of transition metal cyanides with open framework structures. The general chemical formula of PPBAs is AlM. x [M´(CN)6]·yH2O, where A is an alkali metal ion, and M and M´ are transition metal ions. Water of crystallization is typically present on the surface and inside the crystal. When both M1 and M2 are iron, Fe4[Fe(CN)6]3· Z H₂O, commonly known as Prussian blue (FeCNFe), is a metal coordination framework with a face-centered cubic crystal structure and mixed valence states [Fe]. 2+ (CN)6] 4− and Fe 3+ It possesses abundant iron content and is low-cost with controllable shape. This invention discovers that Prussian blue, during high-temperature carbonization, coats the metal compound with a nitrogen-doped carbon layer, effectively improving the material's conductivity. The material prepared by this invention exhibits excellent electrochemical performance and can be used as an electrode material, demonstrating good cycle stability and high capacity in lithium batteries.

[0048] In some embodiments of the present invention, in step (1), the carbon source is glucose, and the mass ratio of glucose to Prussian blue is 0.2-1.0. Specifically, in some embodiments of the present invention, the mass ratio of glucose to Prussian blue is set to 0.2-1.0, 0.4-1.0, 0.6-1.0, 0.8-1.0 and 1.0-1.0, and the resulting materials can all achieve better results. Among them, the material with a mass ratio of glucose to Prussian blue of 0.6-1.0 has the best electrochemical performance.

[0049] In some embodiments of the present invention, in step (1), Prussian blue and carbon source are dispersed in anhydrous ethanol, then placed in an oven at 50-70°C for 4-8 hours, and then annealed under an inert gas atmosphere to obtain Fe3O4@C precursor.

[0050] In some embodiments of the present invention, in step (1), 0.5 g of Prussian blue is dispersed in 4-10 mL of anhydrous ethanol. Specifically, in some embodiments of the present invention, 0.5 g of Prussian blue is dispersed in 4 mL, 6 mL, 8 mL and 10 mL of anhydrous ethanol. The materials obtained can all achieve better results. Among them, the material obtained by using 6 mL of anhydrous ethanol has the best electrochemical performance.

[0051] In some embodiments of the present invention, in step (1), the inert gas atmosphere is specifically an argon atmosphere.

[0052] In some embodiments of the present invention, in step (1), the annealing temperature is 500-800℃. Specifically, in some embodiments of the present invention, annealing is performed at 500℃, 600℃, 650℃, 700℃, 750℃ and 800℃ respectively, with the most preferred temperature being 650℃; the annealing time is 4-7 h. Specifically, in some embodiments of the present invention, annealing is performed at 4 h, 5 h, 6 h and 7 h respectively, with the most preferred time being 5 h.

[0053] In some embodiments of the present invention, in step (2), the Fe3O4@C precursor is added to a reaction vessel containing HF solution for hydrothermal fluorination. The present invention has found that further hydrothermal fluorination yields iron fluoride, where the fluorine source vapor directly contacts the precursor, resulting in a more thorough and gentle reaction process, uniform heat release, and more controllable powder morphology.

[0054] In some embodiments of the present invention, in step (2), the concentration of the HF solution is 30-60 wt%. Specifically, in some embodiments of the present invention, 30 wt%, 40 wt%, 50 wt% and 60 wt% are used respectively, among which 40 wt% of HF solution is the most effective.

[0055] In some embodiments of the present invention, in step (2), the temperature of the hydrothermal fluorination reaction is 90-120°C. Specifically, in some embodiments of the present invention, the temperature of the fluorination reaction is set to 90°C, 100°C, 110°C and 120°C respectively, with 110°C being the most preferred. The time of the hydrothermal fluorination reaction is 3-6 h. Specifically, in some embodiments of the present invention, the time is set to 3 h, 4 h, 5 h and 6 h respectively, with 4 h being the most preferred.

[0056] In some embodiments of the present invention, in step (3), the fluorinated sample in step (2) is washed and centrifuged with ethanol before drying.

[0057] In some embodiments of the present invention, in step (4), the heat treatment temperature is 200-300℃. Specifically, in some embodiments of the present invention, the heat treatment temperature is set to 200℃, 225℃, 250℃, 275℃ and 300℃ respectively, wherein the most preferred heat treatment temperature is 225℃; the heat treatment time is 6-10 h. Specifically, in some embodiments of the present invention, the heat treatment time is set to 6 h, 8 h, 10 h and 12 h respectively, wherein the most preferred heat treatment time is 10 h.

[0058] The following is a specific embodiment and comparative example of the present invention for illustrative purposes.

[0059] Example 1

[0060] (1) By analyzing the balance, 0.50 g of Fe4[Fe(CN)6]3 and 0.30 g of C6H were weighed. 12 O6 powder was dissolved in a mortar containing 6 mL of anhydrous ethanol, mixed and ground for 10 min, placed in a 60℃ forced-air oven for 6 h, removed and placed in a tube furnace, and annealed at 650℃ for 6 h under an argon atmosphere with a heating rate of 5℃ / min to obtain the Fe3O4@C precursor.

[0061] (2) Place 0.10 mg of the precursor in a 20 mL open polytetrafluoroethylene liner, then pour 10 mL of 40 wt% HF solution into a 100 mL polytetrafluoroethylene liner, and place the above small polytetrafluoroethylene liner in it. React at 110 °C for 4 h. After the reaction vessel cools to room temperature, remove it, wash it with anhydrous ethanol, centrifuge it three times, and dry it in a vacuum oven at 60 °C to obtain FeF3·3H2O@C rich in water of crystallization.

[0062] (3) FeF3·3H2O@C was placed in a tube furnace and annealed at 225℃ for 10 h at a heating rate of 5℃ / min to remove some of the water of crystallization, thus obtaining FeF3·0.33H2O@C containing a small amount of water of crystallization.

[0063] The microstructure characterization results of the FeF3·0.33H2O@C material prepared in this embodiment are as follows:

[0064] (1) By Figure 2As can be seen, the XRD pattern of the FeF3·0.33H2O@C material in Example 1 shows that all diffraction peaks of the synthesized material point to FeF3·0.33H2O in JCPDS NO.76-1262. The diffraction peak intensity is weak, indicating that its crystallinity is low. The diffraction peaks also show a broadening phenomenon, indicating that the synthesized FeF3·0.33H2O@C material should be small-sized nanoparticles.

[0065] (2) By Figure 3 It can be seen that the FeF3·0.33H2O@C material in Example 1 contains F, Fe, C and O elements.

[0066] (3) By Figure 4 It can be seen that the FeF3·0.33H2O@C material in Example 1 has a spherical morphology similar to that of a bayberry, with rod-shaped carbon loaded on the surface, which effectively suppresses the volume expansion of the iron fluoride material during the charging and discharging process.

[0067] (4) By Figure 6 It can be seen that, compared with FeF3·0.33H2O without carbon coating, the FeF3·0.33H2O@C material in Example 1 has a carbon content of 17.41% and a fluoride content of 82.99%.

[0068] The FeF3·0.33H2O@C material from Example 1 was applied as a cathode material in a lithium-ion battery. The specific steps are as follows:

[0069] Preparation of FeF3·0.33H2O@C electrode and battery

[0070] FeF3·0.33H2O@C, conductive agent Ketjen black, and binder polyvinylidene fluoride from Example 1 were mixed in a mass ratio of 8:1:1 and then dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. The slurry was then coated onto an aluminum foil with a thickness of 200 μm, dried, and cut into 12 mm discs as positive electrodes. A lithium sheet was used as the counter electrode, a 16 mm PP membrane was used as the separator, and a LiPF6 solution with a concentration of 1 mol / L (EC, DMC, and DEC in a volume ratio of 1:1:1) was used as the electrolyte. The CR2032 button cell was assembled in a glove box filled with argon gas, where the water and oxygen contents were both less than 0.1 ppm.

[0071] Electrochemical performance testing

[0072] (1) Testing was conducted at 289 K using the Xinwei multi-channel CT-4008-5V20mA testing system. Within a voltage range of 1.7-4.2 V, 100 mAh g... -1The assembled battery was tested for cycle capacity and coulombic efficiency at a constant current density; similarly, at a constant voltage range, the efficiency was tested at 1000 mAh g⁻¹. -1 High current cycling capacity and coulombic efficiency were tested at current density.

[0073] (2) Testing was conducted at 289 K using the Xinwei multi-channel CT-4008-5V20mA test system. Within the voltage range of 1.7-4.2 V, at 100 mA g... -1 200 mA g -1 500 mA g -1 1000 mA g -1 2000 mA g -1 500mA g -1 and 100 mA g -1 The rate performance was tested by cycling each current density five times.

[0074] (3) Tests were performed at 289 K using a Shanghai Huachen electrochemical workstation. Cyclic voltammetry tests were conducted within a voltage range of 1.7-4.2 V at scan rates of 0.1, 0.2, 0.4, 0.6, 0.8, and 1 mV / s.

[0075] (4) Tests were conducted at 289 K using a Shanghai Huachen electrochemical workstation. At 0.01 Hz-10 5 Impedance testing was performed within a frequency range of Hz.

[0076] like Figure 7 and 8 The results are shown below: When used as a positive electrode in lithium-ion batteries, the active material loading is ~1 mg cm⁻¹. -2 Within a voltage window of 1.7–4.2 V, at 100 mA g -1 At the current density, the initial discharge specific capacity is 249.17 mAh g. -1 After 100 cycles, the discharge capacity was 148.48 mAh g. -1 ; at 2000 mA g -1 At the current density, the initial discharge capacity is 135.55 mAh g. -1 After 100 cycles, the discharge capacity was 119.60 mAh g. -1 The capacity retention rate was 88.59%.

[0077] at 100 mA g -1 200 mA g -1 500 mA g -1 1000 mA g -12000 mA g -1 500 mA g -1 and 100 mA g -1 At current densities of [values ​​missing], the average discharge capacities were 200.01, 175.13, 156.21, 147.81, 126.72, 148.5, and 158.23 mAh g⁻¹. -1 .

[0078] Comparative Example 1

[0079] This example provides a method for preparing FeF3·0.33H2O material, which is basically the same as the preparation method in Example 1. The difference is that in step (1), Fe4[Fe(CN)6]3 powder is directly annealed in air at 650°C for 6 h at a heating rate of 5°C / min.

[0080] The microstructure characterization results of the FeF3·0.33H2O material prepared in this comparative example are as follows:

[0081] (1) By Figure 4 It can be seen that the FeF3·0.33H2O material in Comparative Example 1 has a smooth surface and a large size.

[0082] (2) By Figure 5 It can be seen that all the diffraction peaks of the XRD pattern of FeF3·0.33H2O in Comparative Example 1 point to FeF3·0.33H2O of JCPDS No. 76-1262. The strong diffraction peak intensity indicates that it has a high degree of crystallinity and a large sample size.

[0083] The FeF3·0.33H2O prepared in this comparative example was applied to a lithium-ion battery, and the specific steps were as described in Example 1. Figure 7 As shown, comparing the data of FeF3·0.33H2O material prepared in this comparative example with those of Example 1, it can be seen that FeF3·0.33H2O@C exhibits better discharge capacity and cycle performance. This is because the coated carbon limits the volume expansion of iron fluoride during the charge and discharge process.

[0084] Comparative Example 2

[0085] This example provides a method for preparing FeF3·0.33H2O@C-2, which is basically the same as the preparation method in Example 1, except that: 0.50 g of Fe4[Fe(CN)6]3 and 0.15 g of C6H are weighed using an analytical balance. 12 O6 powder was dissolved in a mortar containing 6 mL of anhydrous ethanol and ground for 10 min to obtain FeF3·0.33H2O@C-2 material.

[0086] The FeF3·0.33H2O@C materials of Example 1, FeF3·0.33H2O of Comparative Example 1, and FeF3·0.33H2O@C-2 of Comparative Example 2 were applied to lithium-ion batteries, and the specific steps were as described in Example 1. The results are shown below:

[0087] Figure 7 (a) shows the voltage range of 1.7–4.2 V, 100 mA g -1 The discharge capacity and coulombic efficiency measured at current density show that the average initial discharge capacity of the three materials is 220 mAh g⁻¹. -1 However, after 100 cycles, the discharge capacity of FeF3·0.33H2O@C (148.32 mAh g) was... -1 The concentration was significantly higher than that of FeF3·0.33H2O@C-2 (126.71 mAh g). -1 ) and FeF3·0.33H2O (100.93 mAh g) -1 Furthermore, the FeF3·0.33H2O@C material exhibits a relatively low capacity decay rate during 100 charge-discharge cycles. Figure 7 (b) shows the concentration at 1000 mA g -1 The discharge capacity and coulombic efficiency measured at the current density show that the electrochemical performance of FeF3·0.33H2O@C remains excellent, with an initial discharge specific capacity of 164.73 mAh g⁻¹. -1 After 100 cycles, the discharge capacity was 124.34 mAh g. -1 The coulombic efficiency is close to 100%, and the discharge capacity after 100 cycles of FeF3·0.33H2O@C-2 is 107.23 mAh g. -1 The discharge capacity of FeF3·0.33H2O after 100 cycles is 76.89 mAh g. -1 . Figure 7 (c) FeF3·0.33H2O@C materials (200.01, 175.13, 156.21, 147.81, 126.72, 148.5 and 158.23 mAh g) -1 ) at 100 mA g -1 200 mA g -1 500 mA g -1 1000 mA g -1 2000mA g -1 500 mA g -1 and 100 mA g -1The discharge capacity at the specified current densities is superior to that of FeF3·0.33H2O@C-2 material (197.43, 148.94, 131.11, 122.32, 100.72, 131.25, 162.43 mAh g⁻¹). -1 ) and FeF3·0.33H2O materials (113.61, 92.81, 80.86, 78.6, 65.1, 64.44, 91.99 mAh g) -1 ).

[0088] Figure 7 (d) shows the three materials FeF3·0.33H2O@C, FeF3·0.33H2O@C-2, and FeF3·0.33H2O under the test conditions of amplitude 5 mV and 0.01 Hz-10. 5 An AC impedance spectrum is measured in the Hz frequency range. It mainly consists of a semicircle and a straight line. The high-frequency region contains an impedance R representing the charge transfer response. ct The straight line in the low-frequency region represents the Warburg impedance Z of lithium ion diffusion in the solid-phase active material. w If the chemical system is kinetically slow, it will exhibit a large R0. ct It will be represented by the diameter of the semicircle, if R ct Much smaller than the Warburg impedance. Such a system is kinetically fast, appearing as a straight line at an angle to the real axis in the impedance spectrum. The figure shows the R of the FeF3·0.33H2O@C material. ct The Ω is 106.8, and the material R is FeF3·0.33H2O@C-2. ct The material R is 231.1Ω, FeF3·0.33H2O. ct The Ω value is 247.6, indicating that the FeF3·0.33H2O@C material has better conductivity than the other two materials. Furthermore, the slope of the linear curve in the low-frequency region for FeF3·0.33H2O@C is greater than that for FeF3·0.33H2O@C-2 and FeF3·0.33H2O, reflecting that FeF3·0.33H2O@C has a larger lithium-ion diffusion coefficient when used as a cathode material. These data demonstrate that FeF3·0.33H2O@C material exhibits better electrochemical performance.

[0089] Compared with the technical solutions disclosed in the prior art listed in the background section (Chinese Patent CN 114551824 A, hereinafter referred to as Prior Art 1), the solution of this patent is different in both the synthesis process and the material morphology and structure, and the prepared material has better electrochemical performance. The specific comparison is as follows:

[0090] (1) This patented solution uses Prussian blue powder as the iron source and glucose as the carbon source because Prussian blue powder, as a face-centered cubic crystal structure metal coordination framework, has a mixed valence state [Fe]. 2+ (CN)6] 4− and Fe 3+ It has a rich iron content and is low-cost with controllable shape. However, the iron source used in existing literature 1 is the common ferric nitrate nonahydrate compound, and the carbon source is chitosan.

[0091] (2) The required pharmaceuticals for this patented method are relatively few, and the carbon coating method is simple. It mainly involves carbonizing glucose by grinding and then coating it onto the surface of Prussian blue powder. In contrast, the coating method in existing literature 1 involves not only carbon and iron sources, but also a two-phase mixture of sorbitan trioleate and isooctane, as well as the presence of disodium ethylenediaminetetraacetate chelating agent, making the synthesis process complicated.

[0092] (3) The FeF3·0.33H2O@C synthesized in this patent has a higher content of iron fluoride than the FeF3·0.33H2O@C material synthesized in existing literature 1. The iron fluoride content in the material synthesized in this patent application is 82.99 wt%, while the iron fluoride content in the material synthesized in existing literature 1 is only 39.04 wt%.

[0093] (4) The FeF3·0.33H2O@C material synthesized by this patent scheme has better electrochemical performance, with an initial discharge capacity of 135.55 mAh g at a discharge rate of 2 C. -1 After 200 cycles, the discharge capacity was 108.70 mAh g. -1 The capacity retention rate was 80.51%, indicating good fast charging capability. In contrast, the FeF3·0.33H2O@C material synthesized in existing literature 1 exhibited a first-cycle charge / discharge capacity of 153 mAh g⁻¹ at a rate of 0.2 C. -1 After 200 cycles, the discharge specific capacity remains at 119 mAh g. -1 The energy efficiency can reach 85%. It is worth noting that the FeF3·0.33H2O@C material synthesized in this patent is fast-charged at a current density (2 C) ten times higher than that of the comparative example, and has good fast-charging capability; while existing literature 1 only provides cycling performance at a low current (0.2 C).

[0094] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a Prussian blue-derived iron fluoride@carbon composite material, characterized in that, Includes the following steps: (1) Using Prussian blue as the iron source, it is mixed evenly with carbon source and then heat-treated to obtain Fe3O4@C precursor; (2) Fluoride the Fe3O4@C precursor obtained in step (1); (3) The fluorinated sample from step (2) was dried in a vacuum oven at 50-90℃ to obtain a fluorinated iron@C composite material containing water of crystallization; (4) The dried sample was heat-treated to remove some of the water of crystallization and FeF3·0.33H2O@C material was obtained, which is the Prussian blue-derived iron fluoride@carbon composite material; In step (1), Prussian blue and carbon source are dispersed in anhydrous ethanol and then placed in an oven at 50-70°C for 4-8 hours. Then, under an inert gas atmosphere, they are annealed at 500-800°C for 4-8 hours to obtain Fe3O4@C precursor.

2. The method for preparing the Prussian blue-derived iron fluoride@carbon composite material according to claim 1, characterized in that: In step (1), the carbon source is glucose, and the mass ratio of glucose to Prussian blue is 0.2-1.

0.

3. The method for preparing the Prussian blue-derived iron fluoride@carbon composite material according to claim 1, characterized in that: In step (2), the Fe3O4@C precursor is added to a reactor containing HF solution for hydrothermal fluorination.

4. The method for preparing the Prussian blue-derived iron fluoride@carbon composite material according to claim 3, characterized in that: In step (2), the concentration of HF solution is 30-60 wt%, the temperature of fluorination reaction is 90-120℃, and the time is 3-6 h.

5. The method for preparing the Prussian blue-derived iron fluoride@carbon composite material according to claim 1, characterized in that: In step (3), the fluorinated sample from step (2) is washed and centrifuged with ethanol before drying.

6. The method for preparing the Prussian blue-derived iron fluoride@carbon composite material according to claim 1, characterized in that: In step (4), the heat treatment temperature is 200-300℃ and the time is 6-12 h.

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