Preparation of Mo-doped FeSe2 electrode material and application of Mo-doped FeSe2 electrode material in sodium ion battery

Abstract

The invention provides a preparation method of a Mo-doped FeSe2 electrode material and application of the Mo-doped FeSe2 electrode material as a sodium-ion battery anode, and the preparation method comprises the following steps: mixing FeCl3. 6H2O, terephthalic acid and N, N-dimethylformamide, loading into a reaction kettle, and heating at high temperature to obtain an MIL-88B metal organic framework precursor; and then dispersing the MIL-88B precursor, sodium molybdate, selenium powder and hydrazine hydrate in a solvent, and doping Mo atoms into a FeSe2 electrode material through hydrothermal synthesis to obtain the Mo-FeSe2 sodium ion battery anode. According to the preparation method, Mo atoms are doped into FeSe2, so that the strength of Fe-Se bonds is enhanced, the structure collapse effect of the electrode material is effectively relieved from the structure level, an SEI film on an electrode liquid interface is compact and uniform, and the multiplying power and the cycle service life of the electrode material are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology for sodium-ion batteries, and particularly to a method for preparing Mo-doped FeSe2 electrode material and its application. Background Technology

[0002] Sodium-ion batteries, as a potential low-cost alternative to lithium-ion batteries, have attracted widespread attention due to the abundance, wide distribution, and low cost of sodium resources. Developing anode materials with high specific capacity, excellent cycle stability, and good rate performance is one of the core challenges in realizing the practical application of sodium-ion batteries.

[0003] Iron diselenide (FeSe2), with its high theoretical specific capacity, relatively suitable sodium ion intercalation potential, and the abundance of iron and selenium in the Earth's crust, is considered one of the most promising anode materials for sodium-ion batteries. However, FeSe2 faces significant challenges during charge and discharge: First, repeated sodium ion intercalation / deintercalation causes drastic volume expansion / contraction of the FeSe2 lattice, leading to material pulverization, electrode detachment from the current collector, and ultimately rapid capacity decay. Second, the drastic volume changes and inherent structural instability disrupt the stability of the electrode / electrolyte interface, resulting in continuous and uneven growth and rupture of the solid electrolyte interphase (SEI) film. Furthermore, adverse phase transitions and irreversible side reactions may occur during charge and discharge. These factors collectively limit the cycle life and rate performance of FeSe2 electrodes.

[0004] Metal atom doping is one of the effective strategies for optimizing the performance of iron diselenide (FeSe2) anodes. By introducing specific metal atoms (such as cobalt, nickel, manganese, molybdenum, and titanium) to modify FeSe2, its crystal structure and electronic properties can be effectively controlled. Doped atoms act like wedges, enhancing the mechanical strength of the crystal lattice and partially buffering the stress caused by sodium ion insertion / extraction, thereby significantly reducing volume expansion and maintaining the integrity of the electrode structure. Simultaneously, doping optimizes the electronic conductivity of the material, promotes charge transport, and improves rate performance; more importantly, it stabilizes the FeSe2 crystal framework, suppressing unfavorable phase transitions and side reactions. Crucially, this improved structural stability and effective mitigation of volume expansion directly translate to the electrode / electrolyte interface: it facilitates the formation of a thinner, denser, and more uniform SEI film during the initial cycling process. A stable SEI film effectively prevents the continuous decomposition of the electrolyte, reduces the irreversible consumption of active sodium, and significantly reduces the need for SEI film rupture and reconstruction due to volume changes in subsequent cycles. Therefore, metal atom doping not only improves the stability of the material from the bulk structure, but also greatly improves the interfacial stability, coulombic efficiency and long cycle life of the FeSe2 electrode by promoting the formation and maintenance of a high-quality SEI film.

[0005] In summary, metal atom doping is a key approach to improving the electrochemical performance (especially cycle stability and rate performance) of iron diselenide as a negative electrode material in sodium-ion batteries. The core of this invention lies in providing a specific metal-doped (molybdenum-doped) FeSe2 material and its preparation method, aiming to achieve a comprehensive improvement in the aforementioned performance. Summary of the Invention

[0006] To address the technical problems mentioned in the background section, an innovative method for preparing Mo-doped FeSe2 electrode material and its application in sodium-ion batteries is proposed. The synthesis scheme is highly efficient and uses abundant raw materials, making it suitable for large-scale use in the field of sodium-ion batteries and an ideal electrode material.

[0007] To achieve the above objectives, the present invention provides a method for preparing Mo-doped FeSe2 electrode material, comprising the following steps:

[0008] Step 1, Preparation of MIL-88B precursor: Commercial FeCl3·6H2O, terephthalic acid, and NaOH solid were dispersed in N,N-dimethylformamide (DMF). The reaction was carried out at a constant temperature of 100°C for 12 hours. After centrifugation, washing, and drying, the metal-organic framework MIL-88B was obtained.

[0009] Step 2, Preparation of Mo-FeSe2: The prepared MIL-88B and commercial Na2MoO4·2H2O were dispersed in a mixed solution of ethanol and distilled water to obtain solution A. Simultaneously, selenium powder was dissolved in hydrazine hydrate to obtain solution B. Solutions A and B were mixed thoroughly and reacted at a constant temperature of 200℃ for 20 hours. After centrifugation, washing, and drying, Mo-FeSe2 was obtained.

[0010] As a further description of the above technical solution:

[0011] In step one, the molar concentration of FeCl3·6H2O is preferably 5.0–18.0 mmol / L, and the molar concentration of terephthalic acid is preferably 5.0–23.0 mmol / L.

[0012] As a further description of the above technical solution:

[0013] In step two, the type of molybdate is not limited, including one or more of sodium molybdate, ammonium molybdate, etc., but sodium molybdate is preferred, and the molar concentration of molybdenum ions in solution A is preferably 0.50 to 1.55 mol / L.

[0014] As a further description of the above technical solution:

[0015] In step two, the type of solvent is not limited, including distilled water and organic solvents. Organic solvents include, but are not limited to, one or more of ethanol, methanol, and DMF, but ethanol is the most preferred.

[0016] As a further description of the above technical solution:

[0017] In step two, the ratio of distilled water to organic solvent is not limited, but the optimal volume ratio is distilled water: organic solvent equal to (1.0~3.5):1, and ethanol is selected as the organic solvent.

[0018] As a further description of the above technical solution:

[0019] In step two, the molar concentration of commercial selenium powder in solution B is preferably 0.34–1.77 mmol / L.

[0020] As a further description of the above technical solution:

[0021] In step two, the selenization temperature is preferably 130~240℃, and the time is preferably 12~26h.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] 1. In this invention, Mo-doped FeSe2 materials were prepared through a simple solvothermal reaction combined with a selenization process, providing an effective strategy for studying the structural stability and interfacial chemical behavior of layered metal selenides in sodium-ion batteries (SIBs) regulated by Mo doping. The key role of doped metal atoms in mitigating volume expansion during sodium ion insertion / extraction and their catalytic regulation of the solid electrolyte interphase (SEI) formation process were investigated in detail. The results show that Mo doping effectively enhances the mechanical stability of the FeSe2 lattice, significantly suppresses volume changes during charge and discharge, and catalyzes and accelerates the decomposition kinetics of electrolyte components, promoting the formation of an SEI film rich in stable inorganic components (such as NaF, Na2CO3, etc.), thereby reducing interfacial impedance and improving sodium ion transport efficiency.

[0024] 2. The Mo-FeSe2 electrode material prepared in this invention exhibits significant advantages in electrochemical performance. Benefiting from the improved structural stability and optimized interfacial ion transport brought about by doping, this material demonstrates high specific capacity, excellent rate performance, and long cycle life. Specifically, at a current density of 0.5 A / g, the material exhibits a reversible specific capacity as high as 535 mAh / g, with an initial coulombic efficiency exceeding 83.52%, effectively reducing active sodium loss. Even at a high current density of 20 A / g, it maintains a specific capacity of 315 mAh / g, demonstrating excellent rate performance. More importantly, after 4000 constant current charge-discharge cycles at a current density of 5.0 A / g, the capacity retention rate is as high as 90.01% (significantly better than undoped FeSe2), fully demonstrating the excellent effect of doping in suppressing structural degradation and improving cycle stability.

[0025] 3. The preparation method employed in this invention is simple and effective, and the raw materials are abundant and inexpensive. The hydrothermal selenization process is concise and efficient, with the core step being a one-pot hydrothermal selenization process. It is easy to operate, requires no complex equipment or stringent conditions, and is readily scalable for large-scale production. The core raw materials, iron (Fe) and selenium (Se), are relatively abundant in the Earth's crust, and molybdenum, the dopant, is also a common and cost-effective element. The material system of this invention effectively reduces raw material costs and energy consumption, providing a practical solution for developing high-performance and economically competitive sodium-ion battery anode materials. Attached Figure Description

[0026] Figure 1 A scanning electron microscope image of MIL-88B provided according to Embodiment 1 of the present invention is shown;

[0027] Figure 2 A scanning electron microscope image of Mo-FeSe2 provided according to Embodiment 1 of the present invention is shown;

[0028] Figure 3 The image shown is a transmission electron microscope image of Mo-FeSe2 in high-angle annular dark-field mode according to Embodiment 1 of the present invention;

[0029] Figure 4 The X-ray diffraction patterns of FeSe2 and Mo-FeSe2 provided according to Embodiment 1 of the present invention are shown;

[0030] Figure 5 The electrochemical performance of Mo-FeSe2 as an electrode material in an ether-based electrolyte, as shown in Example 1 of the present invention, is illustrated. Figure 5 a is the charge-discharge curve for the first 10 cycles at a current density of 0.5 A / g. Figure 5 b is the charge-discharge performance curve graph under different current densities. Figure 5c is the result of the cycle stability test of Mo-FeSe2 as electrode material at a current density of 5A / g;

[0031] Figure 6 The charge-discharge curves of the full cell prepared according to Example 1 of the present invention, using Mo-FeSe2 as the anode and Na3V2(PO4)3@C as the cathode, are shown for the first 5 cycles at a current density of 0.2 A / g.

[0032] Figure 7 The electrochemical performance diagram of a full cell prepared according to Example 1 of the present invention, using Mo-FeSe2 as the anode and Na3V2(PO4)3@C as the cathode, is shown. Figure 7 a represents the rate performance at the same current density. Figure 7 Figure b shows the cycle stability test results at a current density of 1 A / g; Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] Please see Figure 1-7 This embodiment provides a method for preparing a metal-doped modified Mo-FeSe2 electrode material and its application, including the following steps:

[0036] Step 1: First, Fe-based MIL-88B was synthesized using a hydrothermal method. The specific steps are as follows: 1.620 g (6 mmol) of ferric chloride hexahydrate (FeCl3·6H2O) and 0.996 g (6 mmol) of 1,4-phthalic acid (BDC) were dispersed in 60 mL of N,N-dimethylformamide (DMF), and 2.0 mL of 2 M sodium hydroxide (NaOH) solution was added. The mixture was stirred for 20 minutes, then transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and heated at 100°C for 12 hours. After naturally cooling to room temperature, the orange solid product was recovered by centrifugation. The collected solid was washed three times each with DMF and acetone, alternating between the two. Finally, the MIL-88B nanoparticles were vacuum-dried overnight at 60°C to obtain the product; the scanning electron microscope image is shown below. Figure 1 As shown.

[0037] Step 2: 200 mg of MIL-88B precursor and 160 mg of sodium molybdate dihydrate (Na₂MoO₄·2H₂O) were uniformly dispersed in a mixed solvent of 10 mL ethanol and 25 mL deionized water, labeled as solution A. Separately, 52.24 mg of selenium powder was dissolved in 3.3 mL of hydrazine hydrate (N₂H₄·H₂O) and stirred for 12 hours to form solution B. Solution B was then added dropwise to solution A, and the mixture was stirred for another 30 minutes. The mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated in an oven at 200°C for 20 hours. After naturally cooling to room temperature, the precipitate was collected, washed twice alternately with ethanol and deionized water, and then vacuum dried overnight at 60°C. The resulting product was labeled Mo-FeSe₂, and its scanning electron microscopy morphology is shown below. Figure 2 As shown, the doped Mo atoms can be obtained from Figure 3 Observed.

[0038] The X-ray diffraction pattern of Mo-FeSe2 obtained by the above steps is as follows: Figure 4 As shown.

[0039] The Mo-FeSe2 prepared above was used as the negative electrode material for a sodium-ion battery, and its electrochemical performance was tested in an ether-based electrolyte solution. Figure 5 As shown. Figure 5 a is the charge-discharge curve for the first 10 cycles at a current density of 0.5 A / g. Figure 5 b shows the charge-discharge curves at different current densities. Figure 5 c shows the cycle stability test at a current density of 5 A / g. After 4000 charge-discharge cycles, the capacity retention rate is still 90.01%.

[0040] The Mo-FeSe2 prepared above was used as the negative electrode material for a sodium-ion battery, and Na3V2(PO4)3@C was used as the positive electrode material. The electrochemical performance of the full battery was tested in an ether-based electrolyte solution. Figure 6 and Figure 7 As shown. Figure 6 The chart shows the charge-discharge curves for the first 5 cycles at a current density of 0.2 A / g. Figure 7 The graphs show the rate performance and stability at different current densities. After 300 constant current charge-discharge cycles at a current density of 0.2 A / g, the capacitance retention rate of the electrode material is close to 100%.

[0041] Example 2

[0042] Step one: First, Fe-based MIL-88B is synthesized using a hydrothermal method. The specific steps are the same as in Example 1.

[0043] Step 2: 200 mg of the MIL-88B precursor was uniformly dispersed in a mixed solvent of 10 mL ethanol and 25 mL deionized water, labeled as solution A. Separately, 52.24 mg of selenium powder was dissolved in 3.3 mL of hydrazine hydrate (N₂H₄·H₂O) and stirred for 12 hours to form solution B. Solution B was then added dropwise to solution A, and the mixture was stirred for another 30 minutes. The mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and heated in an oven at 200°C for 20 hours. After naturally cooling to room temperature, the precipitate was collected, washed twice alternately with ethanol and deionized water, and then vacuum dried overnight at 60°C. The resulting product was labeled as FeSe₂. The scanning electron microscope morphology was similar to... Figure 2 The differences are significant; the specific surface area is noticeably smaller, and it appears as small particles.

[0044] FeSe2 has a specific capacity of 405 mAh / g at 0.5 A / g and 248 mAh / g at 20 A / g.

[0045] Example 3

[0046] Step one: First, Fe-based MIL-88B is synthesized using a hydrothermal method. The specific steps are the same as in Example 1.

[0047] Step 2: 200 mg MIL-88B and 80 mg sodium molybdate dihydrate (Na2MoO4·2H2O) precursor were uniformly dispersed in a mixed solvent of 10 mL ethanol and 25 mL deionized water, labeled as solution A. Separately, 52.24 mg selenium powder was dissolved in 3.3 mL hydrazine hydrate (N2H4·H2O) and stirred for 12 hours to form solution B. Solution B was then added dropwise to solution A, and the mixture was stirred for another 30 minutes. The mixture was transferred to a 100 mL PTFE-lined stainless steel autoclave and heated in an oven at 200°C for 20 hours. After naturally cooling to room temperature, the precipitate was collected, washed twice alternately with ethanol and deionized water, and vacuum dried overnight at 60°C. The resulting product was labeled Mo-FeSe2-1, and its morphology under scanning electron microscopy was similar to... Figure 2 Similar, but the sheet-like structure is thinner.

[0048] Mo-FeSe2-1 has a specific capacity of 442.68 mAh / g at 0.5 A / g.

[0049] Example 4

[0050] Step one: First, Fe-based MIL-88B is synthesized using a hydrothermal method. The specific steps are the same as in Example 1.

[0051] Step 2: 200 mg MIL-88B and 240 mg sodium molybdate dihydrate (Na2MoO4·2H2O) precursor were uniformly dispersed in a mixed solvent of 10 mL ethanol and 25 mL deionized water, labeled as solution A. Separately, 52.24 mg selenium powder was dissolved in 3.3 mL hydrazine hydrate (N2H4·H2O) and stirred for 12 hours to form solution B. Solution B was then added dropwise to solution A, and the mixture was stirred for another 30 minutes. The mixture was transferred to a 100 mL PTFE-lined stainless steel autoclave and heated in an oven at 200°C for 20 hours. After naturally cooling to room temperature, the precipitate was collected, washed twice alternately with ethanol and deionized water, and then vacuum dried overnight at 60°C. The resulting product was labeled Mo-FeSe2-2, and its morphology under scanning electron microscopy was similar to... Figure 2 Similar, but the sheet-like thickness is greater.

[0052] Mo-FeSe2-2 has a specific capacity of 452.12 mAh / g at 0.5 A / g.

[0053] This invention provides a method for preparing molybdenum-doped iron diselenide (Mo-FeSe2) anode material for sodium-ion batteries. Its core innovation lies in solving the volume expansion and interfacial transport bottlenecks through a synergistic mechanism of MOF template guidance and metal doping. Using Fe-based MIL-88B as a precursor, a metal-atom-doped iron diselenide (Mo-FeSe2) electrode material is prepared by one-step hydrothermal selenization. In this design, molybdenum atoms significantly suppress the volume expansion caused by sodium ion insertion / extraction; simultaneously, the molybdenum active sites catalytically regulate SEI film formation, promoting the generation of highly stable inorganic components such as NaF and Na2CO3, reducing interfacial impedance by more than 30%. The Mo doping strategy demonstrates significant effects in suppressing structural degradation and improving cycle life. Therefore, the Mo-FeSe2 electrode material is highly suitable for the battery field and is an ideal electrode material.

[0054] The above description is a specific illustration of the embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can make equivalent substitutions (such as selecting different Fe-based MOFs or different iron salts as iron sources, doping with other metal elements such as Co, Ni, In, Ru, Ti, or adjusting selenization process parameters) or adaptive changes within the scope of the technical principles and core concepts disclosed in the present invention—namely, using MOF precursor templates to guide synthesis and combining metal doping (such as Mo) to synergistically enhance structural stability (suppress volume expansion), catalytically optimize SEI film formation, improve electrochemical performance (high capacity, high rate, long cycling) and reduce costs—all of which should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing Mo-doped FeSe2 electrode material, characterized in that, Includes the following steps: Step 1, Preparation of MIL-88B microrods: First, 1.620 g FeCl3·6H2O, 0.996 g terephthalic acid, and NaOH were dispersed in 60 mL N,N-dimethylformamide and stirred for 20 minutes. Second, the resulting suspension was poured into a polytetrafluoroethylene-lined autoclave and reacted at 100℃ for 12 h. Finally, after cooling to room temperature, the orange solid product was recovered by centrifugation, washed three times alternately with DMF and acetone, and vacuum dried overnight to obtain MIL-88B spindle fibers. Step 2, Preparation of Mo-FeSe2: A solution containing 200 mg MIL-88B and 160 mg Na2MoO4·2H2O was dispersed in 10 mL of ethanol and 25 mL of distilled water. Separately, 52.24 mg of selenium powder was dissolved in 3.3 mL of hydrazine hydrate (N2H4·H2O) and stirred for 12 hours. The two solutions were mixed thoroughly, and the resulting suspension was poured into a 100 mL polytetrafluoroethylene-lined autoclave and heated in an oven at 200°C for 20 hours. After naturally cooling to room temperature, the precipitate was collected, washed twice alternately with ethanol and deionized water, and then vacuum dried overnight at 60°C to obtain Mo-FeSe2.

2. The use of the Mo-doped FeSe2 electrode material according to claim 1 as an electrode material for sodium-ion batteries.

3. The method for preparing a Mo-doped FeSe2 electrode material according to claim 1, characterized in that, In step two, hydrazine hydrate is used as a strong reducing agent, which can reduce metal ions in the solution to the target valence state under high temperature reaction conditions.

4. The method for preparing a Mo-doped FeSe2 electrode material according to claim 1, characterized in that, In step two, the mass ratio of MIL-88B to selenium powder is (1.5-4.0):1, the molar concentration of Na2MoO4·2H2O ranges from 0 to 100 mmol / L, and the reaction time is 10-30 h.

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