Coral-like carbon-coated ferrous fluoride and its preparation method and application

Abstract

The present invention discloses coral-like carbon-coated ferrous fluoride, its preparation method, and application. The preparation method comprises the following steps: Step 1: adding prepared light green FeSiF6.6H2O powder and PAN powder to deionized water, stirring, and then evaporating to obtain a mixed powder of FeSiF6 and PAN; Step 2: pouring the mixed powder into a hollow copper tube, sealing it, and then calcining it in a tube furnace. The present invention provides a simple sealed solid-phase calcination method for in-situ one-step synthesis of trace oxygen-doped carbon-coated coral-like nano-ferrous fluoride (FeF2@C), achieving a balance between nanoparticle size and structural stability for iron-based fluoride conversion materials. The polyacrylonitrile (PAN)-derived carbon coating layer plays a "confinement role," inhibiting the overgrowth of FeF2 grains after agglomeration during battery charge / discharge. Simultaneously, trace oxygen is self-introduced during the closed heat treatment to replace the fluoride ion lattice. The "synergistic effect" of the two effectively enhances the electrochemical performance of the electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of forming material preparation, and in particular to coral-like carbon-coated ferrous fluoride, a preparation method thereof, and an application thereof. Background Art

[0002] Although LIBs have relatively mature technology and market applications, the majority of cathode materials currently used in commercial energy storage and power batteries are still deintercalation-type materials, such as LiCoO2 (LCO), LiFePO4 (LFP), and lithium nickel cobalt manganese oxide (NCM). These cathode materials are limited by their respective theoretical specific capacity limits and the limited resources of cobalt and nickel on Earth, making them difficult to use on a large scale. Meanwhile, in the exploration of SIBs' cathode materials, transition metal oxides, polyanionic compounds, and Prussian blue compounds have garnered widespread attention. However, the large ionic radius of sodium ions, resulting in poor theoretical specific capacity and stability, continue to hinder the practical application of SIBs.

[0003] Compared with the deintercalation type cathode materials of single electron reaction, the conversion type cathode materials of multi-electron conversion reaction have higher theoretical specific capacity, and at the same time can avoid the use of large amounts of precious metals, and have the advantages of low price and low toxicity, so they gradually come into the sight of researchers. The electrode materials currently used for conversion reactions are mainly sulfides, fluorides, metal nitrides, etc., because iron is the fourth most abundant and cheapest metal element on the earth. Taking into account the abundance of elements and actual performance, the typical representatives that are expected to meet the large-scale manufacturing needs of any type of battery are iron-based conversion type cathode materials, namely FeF3 and FeF2. FeF3 has a high charge and discharge rate of up to 712mA hg through a three-electron conversion reaction. -1 However, compared with FeF2, FeF3 will generate more LiF after the conversion reaction (3Li+FeF3→3LiF+Fe), which reduces the reaction kinetics of FeF3, and ultimately leads to the reversible specific capacity of FeF3 after ten cycles being much lower than its theoretical specific capacity. FeF2 has 571mA hg -1 The specific capacity is much higher than that of several mainstream commercial deintercalation cathode materials (e.g., LCO 274mA hg -1 , LPF 170mA hg -1 ), and its average operating voltage of 2.66V corresponds to 1519W hkg -1 Unfortunately, iron-based fluorides exhibit strong insulation due to their large band gap, but also face problems such as a large Fe / LiF interface energy barrier during charging and side reactions between the active material and the electrolyte during charge / discharge. These problems have severely weakened their cycling performance, making it difficult for them to enter the market.

[0004] To address these issues, researchers have adopted strategies such as morphology control, doping, and compounding of active materials, as well as modified electrolyte design, to enhance the performance of iron-based fluoride batteries. For example, FeF3 was composited with polyacrylonitrile (PAN) by electrospinning, and FeF3-carbon composite nanofibers were prepared through subsequent carbonization and fluorination processes. FeF3, combined with the flexibility and conductivity of carbon fibers, can be used as a lithium battery positive electrode to achieve a charge and discharge rate of 100 mA g -1 500mA hg at current density -1 The reversible capacity and the capacity retention rate after 400 cycles were almost 100%. Xiao et al. synthesized monodispersed FeF2 nanorods with a width of about 20 nm by colloid and used them as the positive electrode of lithium battery in an ionic liquid electrolyte (1M LiFSI / Pyr 1,3 After FSI, the capacity retention rate is still >90% after 50 cycles at C / 20.

[0005] It is worth mentioning that due to its poor intrinsic conductivity, the conversion material can achieve the theoretical charge / discharge specific capacity after appropriately reducing the particle size. However, in terms of the preparation process, FeF2 is difficult to maintain chemical stability during the heating process (>600°C). Even under the protection of inert gas, FeF2 is inevitably converted into iron oxide compounds (such as Fe3O4). At the same time, FeF2 grains will also agglomerate and grow. Therefore, how to maintain structural stability while retaining the activity of the material during the preparation process is something worth considering. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing coral-like carbon-coated ferrous fluoride, which achieves a balance between the nanoparticle size and structural stability of the iron-based fluoride conversion material. The polyacrylonitrile (PAN)-derived carbon coating shell plays a "confinement role" to inhibit the overgrowth of FeF2 grains after agglomeration during the battery charge / discharge process. At the same time, trace oxygen is self-introduced during the closed heat treatment to replace the fluoride ion lattice. The "synergistic effect" of the two effectively enhances the electrochemical performance of the electrode.

[0007] In addition, the present invention also discloses coral-like carbon-coated ferrous fluoride and application thereof.

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

[0009] The present invention discloses a method for preparing coralline carbon-coated ferrous fluoride, comprising the following steps:

[0010] Step 1: Add the prepared light green FeSiF6.6H2O powder and PAN powder into deionized water, stir magnetically for 35-45 minutes, and then evaporate to dryness to obtain a mixed powder of FeSiF6 and PAN;

[0011] Step 2: Pour the mixed powder into a hollow copper tube, then seal both ends of the copper tube in a glove box, and then place it in a tube furnace and calcine at 700°C to obtain FeF2@C.

[0012] The specific formation process of FeF2@C is as follows:

[0013] (1) Fe first dissolved in water 2+ Under the action of Coulomb force, FeSiF6.6H2O is adsorbed on the surface of negatively charged PAN particles. After evaporation, FeSiF6.6H2O is tightly attached to the surface of PAN. FeSiF6.6H2O is a block crystal and PAN is a sphere.

[0014] (2) Then, in the initial stage of calcination in a closed space, FeSiF6.6H2O first releases bound water and decomposes into SiF4 gas and FeF2. When the temperature rises to the melting point of PAN, 317°C, PAN rapidly melts under the action of Coulomb force and begins to absorb and embed the nearby positively charged FeF2 grains, and a cyclization reaction occurs at the same time.

[0015] (3) Finally, after reaching 700°C, PAN completes the pyrolysis process and covers the FeF2 particles. At the same time, the bound water evaporated earlier cannot escape and reacts with FeF2 again, introducing trace amounts of oxygen into the fluoride ion lattice. The FeF2 particles are completely confined in the PAN pyrolytic carbon. Finally, each section of carbon-coated FeF2 composite fiber is connected to each other to present a porous cross-linked coral morphology.

[0016] It is further defined that in step 1, light green FeSiF6.6H2O powder and PAN powder are added to deionized water in a mass ratio of 8:1.

[0017] Wherein, in step 1, the magnetic stirring time is 40 minutes.

[0018] The preparation process of the light green FeSiF6.6H2O powder in step 1 is as follows:

[0019] S101: Reduced iron powder and a fluorosilicic acid aqueous solution are mixed and stirred at room temperature for 24 hours to obtain a ferrous fluorosilicic acid aqueous solution (FeSiF6·6H2O) and an excess Fe precipitate according to the following chemical formula;

[0020] Fe + H2SiF6 (acidic solution) → FeSiF6·6H2O (room temperature)

[0021] S102: The FeSiF6·6H2O aqueous solution prepared in S101 was centrifuged to separate the upper light green clear liquid, which was evaporated to dryness at 110°C to obtain light green FeSiF6·6H2O powder.

[0022] The coral-like carbon-coated ferrous fluoride disclosed in the present invention is specifically prepared by adopting the above-mentioned preparation method of coral-like carbon-coated ferrous fluoride.

[0023] The present invention discloses an application of coral-like carbon-coated ferrous fluoride, which is prepared by the above-mentioned preparation method of coral-like carbon-coated ferrous fluoride, and the coral-like carbon-coated ferrous fluoride is used for the positive electrode of lithium-ion batteries and sodium-ion batteries.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adopts a simple sealed solid-phase calcination method to in situ synthesize trace oxygen-doped carbon-coated coralline nano-ferrous fluoride (FeF2@C) in one step, achieving a balance between the nanoparticle size and structural stability of the iron-based fluoride conversion material. The polyacrylonitrile (PAN)-derived carbon coating shell plays a "confinement role", inhibiting the overgrowth of FeF2 grains after agglomeration during the battery charge / discharge process. At the same time, trace oxygen is self-introduced during the closed heat treatment to replace the fluoride ion lattice. The "synergistic effect" of the two effectively enhances the electrochemical performance of the electrode.

[0026] The present invention uses conductive polymer materials polyacrylonitrile (PAN) and ferrous fluoride silicide (FeSiF6.6H2O) as raw materials. Without introducing an additional fluorine source, a one-step high-temperature solid-phase closed calcination method is used to synthesize carbon-coated nano-ferrous fluoride (abbreviated as FeF2@C) with coralline morphology.

[0027] During the heating process, the PAN will melt and embed FeF2 in situ, thereby inhibiting grain growth. After degassing (SiF4) and high-temperature (700°C) carbonization, it will self-cover to form a PAN-derived conductive carbon layer of FeF2. Nano-FeF2 particles are embedded in the coral fibers (diameter of about 40nm). At the same time, trace amounts of oxygen (probably from evaporated bound water) are introduced into the fluoride lattice, achieving two goals at one stroke. During the half-cell test, the cross-linked carbon-based network improved the Li + / Na + The diffusion capacity and the "confinement effect" of the derived carbon layer effectively inhibit the overgrowth of FeF2 grains and improve the conductivity of the active material. In short, the present invention has found the key point to balance the nanoparticle size of FeF2 and structural stability.

[0028] The test results show that FeF2@C as a LIBs cathode material can -1The current density is still 484.96 mA hg after 50 cycles. -1 The reversible specific capacity and capacity retention rate are 91.30%. Meanwhile, FeF2@C as the positive electrode material of SIBs is -1 The current density is 457.98 mA hg in the first discharge -1 The specific capacity is 251mA hg after 20 cycles. -1 Specific capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the preparation and formation process of coral-like FeF2@C and a cross-sectional diagram of the FeF2@C conversion reaction.

[0030] Figure 2a SEM image of FeF2@C at 10k magnification.

[0031] Figure 2b SEM image of FeF2@C at 50k magnification.

[0032] Figure 2c SEM image of FeF2@C at 100k magnification.

[0033] Figure 2d One of the TEM images of FeF2@C.

[0034] Figure 2e This is the second TEM image of FeF2@C.

[0035] Figure 2f HR-TEM image of FeF2@C.

[0036] Figure 2g for Figure 2d EDX image of FeF2@C in a selected area.

[0037] Figure 2h for Figure 2g Distribution of Fe element in the selected area.

[0038] Figure 2i for Figure 2g The distribution of F elements in the selected region.

[0039] Figure 2j for Figure 2g The distribution of C elements in the selected area.

[0040] Figure 2k for Figure 2g The distribution of N elements in the selected region.

[0041] Figure 3aSchematic diagram of the bonding between FeF2 and PAN-derived carbon.

[0042] Figure 3b This is the XRD pattern of FeF2@C.

[0043] Figure 3c Raman images of FeF2@C and PAN-700.

[0044] Figure 3d This is the high-resolution XPS spectrum of Fe.

[0045] Figure 3e High-resolution XPS spectrum of C.

[0046] Figure 3f High-resolution XPS spectrum of F.

[0047] Figure 3g High-resolution XPS spectrum of N.

[0048] Figure 4a FeF2@C as the positive electrode of LIBs in the voltage range of 1-4 V, 100 mA g -1 Galvanostatic charge / discharge curves at different current densities.

[0049] Figure 4b FeF2@C at 0.1mV s -1 The CV curve below.

[0050] Figure 4c FeF2@C under a series of current densities (0.05-1A g -1 ) after normalization of the voltage distribution curve.

[0051] Figure 4d FeF2@C, Nano-FeF2, Micro-FeF2 at 100mA g -1 Comparison of cycling performance and Coulombic efficiency at different current densities.

[0052] Figure 4e FeF2@C, Nano-FeF2 and Micro-FeF2 under a series of current densities (0.05-3A g -1 ) discharge capacity.

[0053] Figure 4f FeF2@C as the positive electrode of SIBs in the voltage range of 1-4.2 V, 20 mA g -1 Galvanostatic charge / discharge curves at different current densities.

[0054] Figure 4g Nano-FeF2 as the positive electrode of SIBs in the voltage range of 1-4.2 V, 20 mA g-1 Galvanostatic charge / discharge curves at different current densities.

[0055] Figure 4h Micro-FeF2 as the positive electrode of SIBs in the voltage range of 1-4.2 V, 20 mA g -1 Galvanostatic charge / discharge curves at different current densities.

[0056] Figure 5a Log(i) and Log(v) graphs of FeF2@C and the redox peak b value after fitting.

[0057] Figure 5b FeF2@C at 0.2mV s -1 Estimated pseudocapacitive contribution at different scan rates.

[0058] Figure 5c The morphology changes of FeF2@C positive electrode after different number of cycles.

[0059] Figure 5d The percentages of capacitance and diffusion-controlled capacity contribution at different scan rates.

[0060] Figure 5e This is the three-dimensional EnergQuist diagram of FeF2@C after different charge / discharge times.

[0061] Figure 5f This is the three-dimensional EnergQuist diagram of Nano-FeF2 after different charge / discharge times.

[0062] Figure 5g This is the three-dimensional EnergQuist diagram of Micro-FeF2 after different charge / discharge times.

[0063] Figure 5h EDS spectra of the separators in FeF2@C and Nano-FeF2 half-cells after 15 charge / discharge cycles.

[0064] Figure 5i Cyclic voltammograms of FeF2@C at different scan rates.

[0065] Figure 5j is the I after fitting of three groups of samples p -v 1 / 2 Slope curve.

[0066] Figure 6a Schematic diagram of two full-battery configurations with FeF2@C positive electrode and PGO negative electrode or LLi negative electrode.

[0067] Figure 6b This is a side view of the pressed PGO negative electrode sheet.

[0068] Figure 6c This is the element distribution diagram of the pressed PGO negative electrode.

[0069] Figure 6d This is the constant current charge / discharge curve of the LLi / FeF2@C full battery.

[0070] Figure 6e This is the constant current charge / discharge curve of the PGO / FeF2@C full battery.

[0071] Figure 6f These are the cycling performance diagrams corresponding to LLi / FeF2@C full battery and PGO / FeF2@C full battery.

[0072] Figure 7 This is a diagram of the state of FeSiF6.6H2O tightly attached to the PAN surface after evaporation.

[0073] Figure 8 This is an electron microscope image of PAN-700 micron carbon spheres containing macropores.

[0074] Figure 9 Zeta potential diagram.

[0075] Figure 10 The X-ray diffraction (XRD) patterns of Nano-FeF2 and Micro-FeF2.

[0076] Figure 11 This is the refinement result of FeF2@C.

[0077] Figure 12 This is the nitrogen adsorption / desorption isotherm diagram.

[0078] Figure 13 This is the overall XPS spectrum of FeF2@C.

[0079] Figure 14 Thermogravimetric diagram of FeF2 per unit mass in FeF2@C.

[0080] Figure 15 Nano-FeF2 and Micro-FeF2 CV curves for lithium batteries.

[0081] Figure 16 Electron micrograph of selected EDS areas.

[0082] Figure 17 This is the constant current charge and discharge curve of lithium-ion battery.

[0083] Figure 18 PAN-700 sodium ion battery constant current charge and discharge curve

[0084] Figure 19 This is the CV test diagram of FeF2@C positive electrode.

[0085] Figure 20a This is the CV test diagram of Nano-FeF2.

[0086] Figure 20b This is the CV test diagram of Micro-FeF2.

[0087] Figure 21 The electron microscope images of Nano-FeF2 electrodes after different number of cycles.

[0088] Figure 22 The electrochemical impedance parameters of the electrode were calculated, as shown in the intercept between the semicircle and the Z axis in the high-frequency region, and the equivalent circuit diagram.

[0089] Figure 23 The electrochemical characteristics of the positive electrode after a series of cycles. DETAILED DESCRIPTION

[0090] Example 1

[0091] This embodiment discloses a method for preparing coral-like carbon-coated ferrous fluoride, comprising the following steps:

[0092] Step 1: Add the prepared light green FeSiF6.6H2O powder and PAN powder into deionized water, stir magnetically for 35-45 minutes, and then evaporate to dryness to obtain a mixed powder of FeSiF6 and PAN;

[0093] Step 2: Pour the mixed powder into a hollow copper tube, then seal both ends of the copper tube in a glove box, and then place it in a tube furnace and calcine at 700°C to obtain FeF2@C.

[0094] The specific formation process of FeF2@C is as follows:

[0095] (1) Fe first dissolved in water 2+ Under the action of Coulomb force, FeSiF6.6H2O is adsorbed on the surface of negatively charged PAN particles. After evaporation, FeSiF6.6H2O is tightly attached to the surface of PAN. FeSiF6.6H2O is a block crystal and PAN is a sphere.

[0096] (2) Then, in the initial stage of calcination in a closed space, FeSiF6.6H2O first releases bound water and decomposes into SiF4 gas and FeF2. When the temperature rises to the melting point of PAN, 317°C, PAN rapidly melts under the action of Coulomb force and begins to absorb and embed the nearby positively charged FeF2 grains, and a cyclization reaction occurs at the same time.

[0097] (3) Finally, after reaching 700°C, PAN completes the pyrolysis process and covers the FeF2 particles. At the same time, the bound water evaporated earlier cannot escape and reacts with FeF2 again, introducing trace amounts of oxygen into the fluoride ion lattice. The FeF2 particles are completely confined in the PAN pyrolytic carbon. Finally, each section of carbon-coated FeF2 composite fiber is connected to each other to present a porous cross-linked coral morphology.

[0098] It is further defined that in step 1, light green FeSiF6.6H2O powder and PAN powder are added to deionized water in a mass ratio of 8:1.

[0099] Wherein, in step 1, the magnetic stirring time is 40 minutes.

[0100] In this embodiment, the preparation process of the light green FeSiF6.6H2O powder in step 1 is as follows:

[0101] S101: Reduced iron powder and a fluorosilicic acid aqueous solution are mixed and stirred at room temperature for 24 hours to obtain a ferrous fluorosilicic acid aqueous solution (FeSiF6·6H2O) and an excess Fe precipitate according to the following chemical formula;

[0102] Fe + H2SiF6 (acidic solution) → FeSiF6·6H2O (room temperature)

[0103] S102: The FeSiF6·6H2O aqueous solution prepared in S101 was centrifuged to separate the upper light green clear liquid, which was evaporated to dryness at 110°C to obtain light green FeSiF6·6H2O powder.

[0104] In addition, the coral-like carbon-coated ferrous fluoride prepared in this embodiment is used as the positive electrode of lithium-ion batteries and sodium-ion batteries.

[0105] In order to facilitate those skilled in the art to further understand the present invention, the present invention is further described below with reference to specific preparation cases.

[0106] (1) 2.4 g of reduced iron powder (CAS 7439-89-6) was mixed with 15.34 g of fluorosilicic acid aqueous solution (H2SiF6, CAS 16961-83-4) and stirred at room temperature for 24 h to obtain an aqueous solution of ferrous fluorosilicic acid (FeSiF6·6H2O) and an excess of Fe precipitate according to the following chemical formula;

[0107] Fe + H2SiF6 (acidic solution) → FeSiF6·6H2O (room temperature)

[0108] (2) After centrifugation of the FeSiF6·6H2O aqueous solution, the upper light green clear liquid was separated and evaporated to dryness at 110°C to obtain light green FeSiF6·6H2O powder;

[0109] (3) 2.4 g of light green FeSiF6·6H2O powder and 0.3 g of polyacrylonitrile (PAN) were mixed in 20 mL of deionized water at a mass ratio of 1:8, stirred for 1 h, and evaporated to dryness at 100 °C;

[0110] (4) In a glove box, 1 g of the evaporated mixed powder was encapsulated in a hollow copper tube 20 cm long and 1.5 cm in diameter. The temperature was then raised to 700 °C at 1 °C / min in a tube furnace under argon protection and kept at this temperature for one hour. The temperature was then naturally cooled to obtain c-FeF2@NC (FeF2 is unstable and easily decomposes at temperatures above 400 °C, and the grains will coarsen. Therefore, it is difficult to prepare FeF2-composite carbon nanomaterials at high temperatures using conventional methods, and additional fluorine sources such as HF and NF3 are often required.

[0111] (5) 1 g of light green FeSiF6·6H2O powder was encapsulated in a 20 cm long and 1.5 cm diameter hollow copper tube. The temperature was then raised to 700°C at 1°C / min in a tube furnace under argon protection and kept at that temperature for one hour. The FeF2-700 was then naturally cooled.

[0112] (6) 1 g of light green FeSiF6·6H2O powder was heated to 200°C at 4°C / min in a tube furnace under argon protection and kept at this temperature for two hours, and then cooled naturally to obtain FeF2-200;

[0113] (7) 1 g of PAN powder was encapsulated in a hollow copper tube 20 cm long and 1.5 cm in diameter. The temperature was then raised to 700 °C at 1 °C / min in a tube furnace under argon protection and kept at this temperature for one hour. The temperature was then naturally cooled to obtain PAN-700.

[0114] like Figure 1 As shown in a, Figure 1 a Schematic diagram showing the synthesis of PAN-derived carbon-coated nanoferrous fluoride (FeF2@C) with coral morphology.

[0115] First, the prepared light green FeSiF6.6H2O powder and PAN powder were added to deionized water at a mass ratio of 8:1. After magnetic stirring for 40 minutes, the mixture was evaporated to dryness to obtain a FeSiF6-PAN mixed powder. Next, to prevent the redox reaction of FeF2 at high temperatures, the mixed powder was poured into a hollow copper tube. The tube was then sealed at both ends in a glove box and calcined at 700°C in a tube furnace to produce FeF2@C.

[0116] Among them, the formation process of FeF2@C can be described as:

[0117] (1) First, Fe2+ dissolved in water is adsorbed on the negatively charged ( Figure 9 ) of the PAN particle surface;

[0118] After evaporation, FeSiF6.6H2O adheres tightly to the PAN surface ( Figure 7 , FeSiF6.6H2O is a block crystal, and PAN is a sphere);

[0119] Figure 7 (a, b) FeSiF6.6H2O crystals (c, d) PAN particles (e, f) FeSiF6.6H2O crystals coated on PAN particles

[0120] (2) Then, in the initial stage of calcination in a closed space, FeSiF6.6H2O first releases bound water and decomposes into SiF4 gas and FeF2. When the temperature rises to the melting point of PAN (317°C), under the action of Coulomb force, PAN quickly melts and begins to absorb the positively charged ( Figure 9 ) of FeF2 grains, and a cyclization reaction occurs simultaneously;

[0121] (3) Finally, after reaching 700°C, PAN completes the pyrolysis process and covers the FeF2 particles. At the same time, the bound water evaporated earlier cannot escape and reacts with FeF2 again, introducing trace amounts of oxygen into the fluoride ion lattice. The FeF2 particles are completely confined in the PAN pyrolytic carbon. Finally, each section of carbon-coated FeF2 composite fiber is connected to each other to present a porous cross-linked coral morphology.

[0122] Generally speaking, increasing the chemical specific surface area by reducing the particle size of FeF2 particles can effectively improve the charge / discharge performance of the electrode material, but this will also weaken the structural stability of the active material, aggravate the agglomeration phenomenon and the adverse reaction between the positive electrode and the electrolyte, and ultimately lead to poor battery stability.

[0123] Therefore, compared with simply reducing the particle size, in the composite FeF2@C, Figure 1 In b, nanometer-sized FeF2 particles are embedded in a PAN-derived carbon matrix. The PAN-derived carbon matrix can effectively enhance the structural toughness of the active material and improve the electronic conductivity, making the discharge process:

[0124] (3Li+FeF2→2LiF+Fe)

[0125] The generated Fe and LiF are confined inside the cavity of carbon fiber, thus avoiding the formation of agglomerated Fe and LiF clusters. On the other hand, the pyridine N after PAN thermal decomposition is beneficial to the Li + / Na + At the same time, the network structure and pore channels of FeF2@C are conducive to the infiltration of electrolyte in electrode materials.

[0126] As controls, FeSiF6.6H2O powder and PAN alone were sealed in copper tubes and calcined at 700°C in the same manner (abbreviated as Micro-FeF2 and PAN-700). In addition, nano-FeF2 (abbreviated as Nano-FeF2) was prepared using FeSiF6 powder at 200°C.

[0127] Figure 2(ak) shows the morphology and element distribution of the FeF2@C sample.

[0128] First, scanning electron microscopy (SEM) images ( Figure 2a -c) It can be seen that the FeF2@C sample is composed of carbon-coated FeF2 nanocomposite fibers with a diameter of about 40 nm. The fibers are cross-linked and form a large number of pore channels, giving the FeF2@C an overall coral-like morphology.

[0129] Then, transmission electron microscopy (TEM) images ( Figure 2d ,e) It can be seen that the composite fiber presents a core-shell structure, and the derived carbon layer covers the surface of the FeF2 nanoparticles. The high-resolution TEM image ( Figure 2f ) shows that the interplanar spacing of about 0.27nm and 0.165nm corresponds to the (101) and (002) planes of FeF2 crystal. Finally, the energy dispersive spectroscopy (EDX) image ( Figure 2g -k) have consistent distribution of Fe, F, C, and N elements, proving that the composite fibers are composed of PAN-derived carbon-coated FeF2.

[0130] In addition, PAN-700 is a micron carbon sphere containing many macropores ( Figure 8 a, b);

[0131] Micro-FeF2 prepared at 700℃ is a dense particle of micron size ( Figure 8 c, d);

[0132] Nano-FeF2 prepared at 200℃ is a nanoparticle with a particle size of about 8-22nm ( Figure 8 e, f), which confirms the conclusion that during high-temperature calcination, individual nano-FeF2 particles will grow into dense micron-FeF2 particles. However, after introducing the thermoplastic material PAN, the nano-FeF2 particles will be in situ embedded in the carbon matrix, and the carbon layer between the particles plays a "confinement" role, thereby alleviating the agglomeration growth of nano-FeF2 particles at high temperatures.

[0133] Figure 8 Medium, (ab)PAN-700, (cd)Micro-FeF2, (ef)Nano-FeF2

[0134] Figure 3(ag) shows the structure and bonding characteristics of the FeF2@C sample.

[0135] first, Figure 3a It is shown that PAN-derived carbon and FeF2 in FeF2@C are tightly bound together by chemical bonds, while the nitrogen-doped conductive carbon layer can improve the material's ability to conduct electrons / ions.

[0136] In addition, Raman spectroscopy was used to analyze the carbon properties in FeF2@C and PAN-700. Figure 3c The D band (approximately 1361 cm -1 ) and G belt (approximately 1582cm -1 ) information, we can find the intensity ratio of D band to G band in FeF2@C (I D / I G ) is higher than that of PAN-700, which indicates that the carbon in FeF2@C is more graphitized due to the catalytic effect of Fe, so FeF2@C has a faster electron conductivity.

[0137] Then, FeF2@C( Figure 3b ), Nano-FeF2 and Micro-FeF2 (see Figure 10 The X-ray diffraction (XRD) pattern in c) shows that FeSiF6.6H2O has been completely converted into FeF2 (JCPDS No.45–1062) and no obvious impurity phase appears.

[0138] Figure 10 XRD patterns of (a) FeSiF6.6H2O, (b) PAN 700, (c) Nano-FeF2 and Micro-FeF2

[0139] By comparing the XRD patterns, it can be found that the characteristic diffraction peak intensity of FeF2 after high temperature sealing and calcination of FeF2@C and Micro-FeF2 becomes stronger and shifts to a higher angle, which indicates that part of the oxygen in the crystal water that cannot escape replaces the fluoride ion, and the crystallinity increases. The Rietveld refinement results were obtained using GSASⅡ software (see Figure 11 , Figure 11 (FeF2@C refinement result), the refinement results show that it contains 0.013wt% FeOF phase after high temperature calcination.

[0140] Scherrer formula calculations show that the particle size of Micro-FeF2 (>100nm) is much larger than that of FeF2@C (55.4nm) and Nano-FeF2 (34.0m), which indicates that PAN melt-coated FeF2 can effectively inhibit the growth of FeF2 grains at high temperatures. Nitrogen adsorption / desorption isotherms of the three groups of samples ( Figure 12) also shows that the specific surface areas of Nano-FeF2 and FeF2@C are 61.181 cm -2 g -1 and 27.214cm -2 g -1 , while the specific surface area of ​​Micro-FeF2 is only 3.960cm -2 g -1 This also confirms that uncoated FeF2 nanoparticles will grow secondary at high temperature, so the chemical specific surface area is smaller.

[0141] Finally, X-ray photoelectron spectroscopy (XPS) characterized the chemical properties of FeF2@C. Figure 13 ) shows that FeF2@C is mainly composed of C, N, Fe, and F elements.

[0142] Fe 2p fine spectrum ( Figure 3d ) at 711.6 eV indicates that Fe may include O-Fe 3+ -F and Fe 2+ -F has two valence states, and the peak at 725.0 eV comes from Fe 2+ 2p 1 / 2 . C 1s fine spectrum ( Figure 3e ) The main peaks at 284.8eV and 286.2eV are attributed to CC and CN of the PAN-derived carbon matrix, and the secondary peak at 289.3eV is attributed to CF, which proves that there is a bonding effect between FeF2 and PAN-derived carbon. Figure 3f ) is attributed to the main peak at 684.9 eV of Fe 2+ -F, the CF peak at 686.2eV once again confirms the close contact between the PAN-derived carbon matrix and FeF2. N 1s fine spectrum ( Figure 3g ) are attributed to pyridine, pyrrole and graphitic nitrogen after PAN thermal decomposition. In addition, Fe and F account for 33.62at% and 33.57at% respectively in XPS. According to the stoichiometric relationship, it is semi-quantitatively calculated that FeOF accounts for 0.025wt% in FeF2, which is close to the refined result.

[0143] XRD, BET and XPS results confirmed that calcination in a closed environment introduced trace oxygen to generate FeOF. At the same time, through the "confinement" effect of PAN-derived carbon, FeF2@C achieved a balance between structural stability and nanoparticle size.

[0144] like Figure 4a-h, before the half-cell test, the FeSiF6.6H2O and PAN were tested by thermogravimetric (TG) in nitrogen, and the content of FeF2 in the unit mass of FeF2@C was estimated to be about 81wt% ( Figure 14 ), and at the same time, we took 1g of FeF2@C and calcined it in air, and the remaining mass (Fe2O3) was 0.7369g, which is about 86.58wt% of FeF2 after conversion. The two results are basically consistent, and the calculation in this paper is based on the latter.

[0145] Then, FeF2@C, Nano-FeF2, Micro-FeF2 and PAN-700 were used as the positive electrodes of LIBs and SIBs, respectively, and then electrochemical tests were carried out at 30°C.

[0146] Figure 4a The results show that FeF2@C can be used as a cathode material for LIBs at 1.0-4.0V (vs Li / Li + ) Voltage range 100mAg -1 The charge / discharge curves of the first three cycles under current, the first discharge capacity is 531.12 mA hg -1 , which is close to the theoretical specific capacity of FeF2, but there is a significant voltage drop when the first discharge reaches 1.68V. The overpotential comes from the disproportionation of conversion iron and the pseudo-intercalation of lithium. The increase in the platform potential after the first discharge may be due to the improved reaction kinetics after the particle size of the regenerated FeF2 particles is reduced. In addition, the first charge capacity of FeF2@C is 463.62mA hg -1 The 19.5% capacity loss may be due to the irreversible side reactions and the formation of solid electrolyte interface (SEI) film during the first discharge process, and the increase in discharge capacity in the first ten cycles may be related to the activation of active materials and solvents.

[0147] At the same time, through 0.1mV s -1 The first three cyclic voltammetry (CV) tests show that in FeF2@C ( Figure 4b ) Two pairs of redox peaks appear (about 3.0 / 3.3 and 2.0 / 2.9 V), which correspond to the intercalation and conversion reactions of FeF2, respectively. At the same time, the peak positions and currents have almost no major changes.

[0148] In comparison, Micro-FeF2( Figure 15 b) has a conversion reaction peak current that is one order of magnitude lower, while Nano-FeF2( Figure 15 The conversion reaction peak of a) decays rapidly in the first three cycles, and the redox potential gap of Micro-FeF2 is about 1.25 V, which is significantly higher than 0.97 V of FeF2@C and 0.93 V of Nano-FeF2.

[0149] Figure 15 CV curves of lithium batteries (a) Nano-FeF2 and (b) Micro-FeF2.

[0150] This result shows that FeF2@C has the most stable electrochemical properties and the best Li storage + power and lowest electrochemical polarization. In addition, Figure 4f The results show that FeF2@C can be used as a cathode material for SIBs at 20 mA g -1 The charge / discharge curves of the first three cycles under current, the first discharge capacity is 432.01mA hg -1 (Theoretical 571mA hg -1 ), after 15 cycles, there is still 290.98mA hg -1 Reversible specific capacity.

[0151] Meanwhile, in the control group, Nano-FeF2 as LIBs ( Figure 17 a) With SIBs positive electrode ( Figure 4g ) Although the first discharge capacity is the highest, it is 640.00mA hg -1 and 497.36mA hg -1 However, it decays rapidly, with only 181.76 mA hg remaining after 50 and 15 cycles respectively. -1 and 35.59mA hg -1 The discharge capacity of LIBs is significantly reduced, and the conversion reaction platform characteristics at 2.1-2.2V completely disappear. Compared with the former, Micro-FeF2 is used as LIBs ( Figure 17 b) with SIBs( Figure 4h )The specific capacity of the positive electrode is not good, and the capacity contributed by PAN can be ignored ( Figure 17 c and Figure 12 ).

[0152] Figure 17 In the figure, (a) is the constant current charge and discharge curve of Nano-FeF2, (b) is the constant current charge and discharge curve of Micro-FeF2, and (c) is the constant current charge and discharge curve of PAN-700.

[0153] Figure 18 This is the constant current charge and discharge curve of PAN-700 sodium ion battery.

[0154] The reason for the difference is precisely because the intrinsic conductivity of fluoride is poor, so the battery performance is heavily dependent on the morphology of the electrode material. Under high temperature conditions, FeF2 nanoparticles will agglomerate and grow into dense FeF2 micron particles, which seriously reduces the electrochemical activity of FeF2, so the Micro-FeF2 capacity is the lowest. Although Nano-FeF2 has the highest first discharge specific capacity, and even exceeds the theoretical value (due to the formation of SEI and electrode side reactions), the accompanying problems such as transition metal dissolution and structural failure will also be more serious in exposed nanoparticles. In contrast, in FeF2@C, on the one hand, the "confinement effect" of the PAN-derived conductive carbon matrix on the nano-FeF2 particles inhibits the dissolution and agglomeration of transition metals and strengthens the structure of the active material;

[0155] On the other hand, the coral-like nanostructure retains the reactivity of FeF2, and the two achieve a balance between nanodesign and structural stability. In addition, the introduction of trace oxygen also improves the intrinsic conductivity of FeF2.

[0156] Therefore, FeF2@C as the positive electrode of LIBs and SIBs respectively exhibits high specific capacity and retention rate ( Figure 4d and 4f ), FeF2@C as the positive electrode of LIBs at 100 mA g -1 After 50 cycles at the same current density, there is still 484.96 mA hg -1 The reversible capacity and obvious conversion reaction platform characteristics, the capacity retention rate is 91.31%. At the same time, it also has a stable charge / discharge curve at different currents ( Figure 4c ), at 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 1.00, 2.00 and 3.00 A g -1 The current densities were 528.27, 478.73, 437.96, 410.12, 387.12, 364.80, 318.51, 264.47 and 223.65 mAh g -1 The reversible specific capacity ( Figure 4e ), showing excellent rate performance.

[0157] To investigate the mechanism of enhanced electrode performance, the present invention employed cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) to compare the electrochemical, elemental, and morphological characteristics of the three groups of samples. The fundamental mechanism of charge storage in battery materials is a limited diffusion-controlled process, generally considered to encompass both surface and diffusion control.

[0158] Therefore, in order to calculate the Li storage capacity of the positive electrode material +During the constant speed step, first use 0.2-1mV s -1 CV test of FeF2@C cathode was carried out at the scan rate ( Figure 19 ).

[0159] As the scan rate changes, it can be clearly found that the peak curves of the CV show similar shapes and positions, which reveals the good and stable electrochemical kinetic performance of the material. The relationship between current (i) and scan rate (v) satisfies the following formula:

[0160] i=av b (1)

[0161] log(i)=log(a)+blog(v) (2)

[0162] At different scan rates, the values ​​of parameters a and b were fitted based on the linear relationship between log(i) and log(v) in the formula. When b = 1, it indicates that the process is dominated by surface control and the capacity comes from the capacitance contribution. When b = 0.5, it indicates that the process is dominated by diffusion control in the bulk phase. If the b value is between 0.5 and 1, it means that the process is controlled by a mixture of surface control and diffusion control. Then, after calculation, the b values ​​of peaks A and B were 0.86 and 0.83 ( Figure 5a ), indicating that the capacity contribution of this process is mixed controlled and dominated by surface control. Finally, the quantitative ratio of the current contribution of surface and diffusion control can be calculated using the following formula:

[0163] i=k1v+k2v 1 / 2 (3) Figure 5c As shown, at 0.2mV s -1 The contribution of the capacitance controlled by the lower surface reaction exceeds 65%, and as the scan rate increases, the diffusion control degree weakens and the capacitance / diffusion ratio gradually increases. -1 This evidence fully demonstrates that the pseudocapacitive process of the electrode is dominated by surface reactions, and the capacity is mainly derived from the rapid redox reaction near the surface active sites. Therefore, the FeF2@C cathode modified by nanocomposite exhibits excellent rate performance.

[0164] Next, use 0.2-1mV s -1 CV test of Li of three groups of samples with the same assembly conditions and battery state + Diffusion capacity ( Figure 5d and Figure 20a , 20b), first according to the peak current of A and B (I p )

[0165] The square root of the scan rate (v 1 / 2 )relation( Figure 5e ) can be found Ip With v 1 / 2 There is a linear correlation between them, which indicates that the redox reaction of FeF2 depends on the diffusion-controlled step, followed by the Randles-Sevcik equation as follows:

[0166] I p =2.69×10 5 n 3 / 2 ACD1 / 2 v 1 / 2

[0167] Where n represents the number of electron transfers, A represents the effective area of ​​the working electrode (cm 2 ), C represents the concentration of ions involved in the redox reaction (mol cm 3 ), D is the diffusion coefficient (cm 2 s -1 ), treat n, A, C as constants, and substitute different v 1 / 2 with I p Then use the fitted function slope to calculate Li + The apparent diffusion coefficient (Na + The diffusion coefficient was calculated using the same method. The results show that + / Na + In the conversion reaction of the process, the Li + / Na + Diffusion ability is from high to low, but in the case of de-Li + / Na + In the conversion reaction of the process, the Li + / Na + The diffusion capacity is the highest, so FeF2@C has the best kinetic performance. This result confirms the previous conclusion that the high crystallinity and conductive carbon coating in FeF2@C enhance the stability of the nanostructure, and the unique coral cross-linking structure and pyrrole N accelerate the Li + / Na + Diffusion ability in solid and liquid phases, all of which are conducive to rapid charge / discharge processes.

[0168] Finally, EIS tests were performed on three groups of samples as LIBs ( Figure 5g -i) and SIBs( Figure 23 )Electrochemical characteristics of the positive electrode after a series of cycles.

[0169] Figure 23 EIS graphs after different numbers of mesocycles in decibels: (a) FeF2@C, (b) Micro-FeF2, (b) Nano-FeF2;

[0170] First, through a simple comparison, we can find that compared with FeF2@C, Micro-FeF2 and Nano-FeF2 as LIBs and SIBs positive electrodes have obvious differences in the semicircle in the high-frequency region, which indicates that the interface and bulk properties of the electrode have changed significantly. Then, a simplified equivalent circuit ( Figure 22 ) The electrochemical impedance parameters of the three groups of electrodes were calculated. The intercepts of the semicircle and the Z axis in the high frequency region were:

[0171] The symbol R represents the resistance related to the current collector, electrolyte, etc. s In the medium-high frequency range, the charge transfer resistance associated with the electrode / electrolyte double layer and the surface layer (SEI) resistance are represented by the symbol R ct With R CEI It is shown that by comparing the attached table 1, it can be found that Micro-FeF2 as the positive electrode of the two batteries has a high R CEI With R ct There was a big increase, and R ct As the number of cycles increases, it may be due to factors such as continuous agglomeration of grains and accumulation of by-products. The same rule is also observed when Nano-FeF2 is used as the positive electrode of LIBs, but when it is used as the positive electrode of SIBs, R CEI With R ct There is a fluctuation that first increases and then decreases. At the same time, the morphology of the Nano-FeF2 electrode after different cycle times ( Figure 21 ) can also be found in the nano-FeF2 particles showed obvious agglomeration phenomenon, and even "over-grew" into large dense particles after 15 cycles, which just reflects the instability of the exposed nanostructure.

[0172] Compared with the first two, FeF2@C has a higher R ct With R CEI The values ​​are much smaller than those of the first two groups of samples, and there is no large fluctuation, which confirms that the coating of highly conductive PAN-derived carbon and the introduction of trace oxygen effectively improve the electron transport capacity of the electrode.

[0173] at the same time Figure 5j It shows that the FeF2@C cathode still maintains the coral-like morphology after multiple cycles. Figure 5f Elemental analysis also shows that on the side of the separator close to the metal lithium in the battery ( Figure 16 The Fe signal of FeF2@C is much weaker than that of Nano-FeF2 in the selected EDS area. These results indicate that during the charge and discharge process, the "confinement" effect of the carbon matrix effectively inhibits the agglomeration, "overgrowth" and transition metal dissolution of the grains, strengthens the coral-like nanostructure, and enables FeF2@C to exhibit stable electrochemical kinetic performance.

[0174] In order to verify the practical applicability of FeF2@C, Figure 6a As shown, a quantitative (64% excess capacity) lithium negative electrode (LLi, Figure 6b ) and pre-lithiated reduced graphite oxide (PGO) after ten cycles in the half-cell were used as the negative electrode of the full battery. Based on the mass of the positive electrode active material, Figure 6d Displayed in the 1.0-4.0V voltage range with 0.10A g -1 At the current density, the first discharge specific energy of LLi / FeF2@C full battery is 976.84Wh kg -1 , which is much higher than the 550Wh kg of LiCoO2 cathode -1 .

[0175] and Figure 6e Displayed in the 0.8-3.0V voltage range with 0.02A g -1 At the current density, the first discharge specific energy of the PGO / FeF2@C full battery is 623.06Wh kg -1 After 20 cycles ( Figure 6f ), the capacity retention rate of the LLi / FeF2@C full battery after the first cycle was 91.65%, which shows that LLi and FeF2@C have good compatibility, but at the same time, the PGO / FeF2@C full battery experienced obvious attenuation in the first ten cycles, which may be due to the irreversible lithium loss induced by the incompatibility of the graphite-based PGO negative electrode with the electrolyte.

[0176] The present invention designs a high-temperature solid-phase closed calcination method, which achieves two goals at one stroke without introducing an additional fluorine source. By utilizing the Coulomb attraction between PAN and FeF2, the polymer material PAN is in situ melt-melted and embedded with FeF2 nanoparticles at high temperature. At the same time, FeF2 in the closed system "self-introduces" trace oxygen, ultimately preparing FeF2@C.

[0177] To address the problems of poor intrinsic conductivity of FeF2, phase separation during charge and discharge, and structural failure, conductive carbon coating and the introduction of trace oxygen bring several benefits.

[0178] First, both improve the electrical conductivity of FeF2 from both the intrinsic and bulk perspectives. Second, carbon coating strengthens the unique coral-like structure of FeF2@C, while the carbon matrix's "confinement" of the nano-FeF2 particles inhibits Fe dissolution and phase separation between Fe and LiF.

[0179] Secondly, trace oxygen replacing fluorine enhances the reversibility of the insertion-conversion reaction. Therefore, FeF2@C maintains high specific capacity while maintaining microstructural and electrochemical stability, achieving a balance between nanoparticle size and structural stability. These properties contribute to FeF2@C's high discharge capacity, stability, and rate capability.

[0180] In LIBs, FeF2@C is -1 At the current density, the first discharge capacity is 531.12 mAh g -1 , and after 50 cycles, there is still 484.96 mAh g -1 Reversible specific capacity, capacity retention rate up to 91.30%, and 3Ag -1 The current density is still 242.50 mAh g -1 Reversible capacity.

[0181] Meanwhile, the first discharge capacity of FeF2@C as the positive electrode of SIBs was 457.98 mAh g -1 After 15 cycles, there is still 251mAhg -1 In addition, LLi / FeF2@C full battery and PGO / FeF2@C full battery showed 976.84Wh kg -1 and 623.06Whkg -1 The reversible specific energy verifies the feasibility of practical application of FeF2.

[0182] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0183] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing coralline carbon-coated ferrous fluoride, characterized in that: The steps include: Step 1: Add the prepared light green FeSiF6.6H2O powder and PAN powder into deionized water, stir magnetically for 35-45 minutes, and then evaporate to dryness to obtain a mixed powder of FeSiF6 and PAN; Step 2: Pour the mixed powder into a hollow copper tube, then seal both ends of the copper tube in a glove box, and then place it in a tube furnace and calcine at 700°C to obtain FeF2@C.

2. The method for preparing coralline carbon-coated ferrous fluoride according to claim 1, wherein: The specific formation process of FeF2@C is as follows: (1) Fe first dissolved in water 2+ Under the action of Coulomb force, FeSiF6.6H2O is adsorbed on the surface of negatively charged PAN particles. After evaporation, FeSiF6.6H2O is tightly attached to the surface of PAN. FeSiF6.6H2O is a block crystal and PAN is a sphere. (2) Then, in the initial stage of calcination in a closed space, FeSiF6.6H2O first releases bound water and decomposes into SiF4 gas and FeF2. When the temperature rises to the melting point of PAN at 317°C, PAN rapidly melts under the action of Coulomb force and begins to absorb and embed the nearby positively charged FeF2 grains, and a cyclization reaction occurs at the same time. (3) Finally, after reaching 700°C, PAN completes the pyrolysis process and covers the FeF2 particles. At the same time, the bound water evaporated earlier cannot escape and reacts with FeF2 again, introducing trace amounts of oxygen into the fluoride ion lattice. The FeF2 particles are completely confined in the PAN pyrolytic carbon. Finally, each section of carbon-coated FeF2 composite fiber is connected to each other to present a porous cross-linked coral morphology.

3. The method for preparing coralline carbon-coated ferrous fluoride according to claim 1, wherein: In step 1, light green FeSiF6.6H2O powder and PAN powder were added to deionized water at a mass ratio of 8:

1.

4. The method for preparing coralline carbon-coated ferrous fluoride according to claim 1, wherein: In step 1, the magnetic stirring time is 40 min.

5. The method for preparing coralline carbon-coated ferrous fluoride according to claim 1, wherein: The preparation process of the light green FeSiF6.6H2O powder in step 1 is as follows: S101： The reduced iron powder and the hydrofluorosilicic acid aqueous solution were mixed and stirred at room temperature for 24 h to obtain the ferrous fluorosilicate aqueous solution and excess Fe precipitate according to the following chemical formula; Fe + H2SiF6→FeSiF6·6H2OS102: The FeSiF6·6H2O aqueous solution prepared in S101 was centrifuged to separate the upper light green clear liquid, which was evaporated to dryness at 110°C to obtain light green FeSiF6·6H2O powder.

6. A coralline carbon-coated ferrous fluoride, characterized in that: The coral-like carbon-coated ferrous fluoride is prepared by the preparation method of coral-like carbon-coated ferrous fluoride according to any one of claims 1 to 5.

7. An application of coralline carbon-coated ferrous fluoride, characterized in that: The coral-like carbon-coated ferrous fluoride prepared by the preparation method of coral-like carbon-coated ferrous fluoride according to any one of claims 1 to 5 is used for the positive electrode of lithium-ion batteries and sodium-ion batteries.

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