Preparation method and application of high-entropy cation and anion co-doped Fe7S8

Abstract

The application discloses a preparation method and application of high-entropy cation and anion co-doped Fe7S8. The application discloses a preparation method of high-entropy cation and anion co-doped Fe7S8, which comprises the following steps: mixing Fe, Ni, Mo, Cr, W, Si, S and Se powders, then performing ball milling, and then placing the powders into a tube furnace to perform high-temperature sulfuration to obtain high-entropy cation and anion co-doped Fe7S8. The application prepares high-entropy cation and single anion co-doped Fe7S8 as a negative electrode material of a sodium ion battery through a simple ball milling-high-temperature sulfuration strategy, so that the capacity and cycle stability of the high-entropy cation doped and single anion co-doped Fe7S8 material are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode materials, specifically to the preparation method and application of Fe7S8 co-doped with high-entropy cations and anions. Background Technology

[0002] In battery systems, electrode materials are the primary contributors to electrochemical performance; therefore, designing and manufacturing electrode materials with high specific capacity, long cycle life, and low cost is crucial for developing next-generation energy storage devices. In lithium-ion batteries, lithium cobalt oxide and graphite, the most widely used positive and negative electrode materials for commercially available rechargeable lithium-ion batteries, have been in use for decades, but they cannot meet increasingly demanding requirements. The growing demand for high-performance energy storage devices, from portable electronic devices to electric vehicles, has spurred research into novel battery technologies beyond lithium-ion. Due to the widespread distribution and abundance of sodium resources, low cost, and environmental friendliness, rechargeable sodium-ion batteries represent a promising alternative to lithium-ion batteries. Sodium-ion batteries possess many advantages that lithium-ion batteries cannot achieve, such as the high abundance and uniform distribution of sodium resources, which can be exploited almost anywhere on Earth; the small solvation radius of sodium ions, requiring less energy for desolvation than lithium ions, resulting in stronger migration capabilities of sodium ions within the electrolyte and at the interface compared to lithium ions; and the ability of inexpensive aluminum foil as a current collector, as aluminum and sodium do not have the conditions for alloying reaction at low potentials, thus reducing costs by using aluminum foil as the negative electrode current collector in sodium-ion batteries.

[0003] For anode materials, the most successful graphite anodes cannot be directly used in carbonate electrolytes and have extremely low sodium storage capacity. Therefore, developing commercially available anode materials is equally urgent and important. Commonly used anode materials for sodium-ion batteries can be broadly classified into intercalated anodes, alloy anodes, and conversion anodes. Among them, intercalated anode materials (i.e., hard carbon, TiO2, and Na2Ti3O7) typically have long cycle life, a smooth redox plateau, and slight volume changes during charge and discharge, but their limited capacity restricts their practicality. Alloy anode materials (i.e., Sn, Sb, and P) have the advantages of large theoretical capacity, low redox potential, and good conductivity. However, these anodes are plagued by huge volume changes, leading to severe structural collapse of the active material. Conversion anode materials (i.e., FeS2, Fe7S8, CoSe2, Sn4P3, and Sb2O3, etc.) typically have larger theoretical capacities than intercalated anode materials and milder volume changes than alloy anode materials, exhibiting excellent overall performance. Therefore, conversion-type anode materials are considered to be potentially excellent anode materials. Among them, transition metal compounds (TMCs), such as oxides and sulfides, show great potential as electrode materials. Among these TMCs, iron sulfide compounds, as one of the representatives of conversion-type materials, are considered to be advanced anode materials due to their high theoretical capacity, small electrode polarization, abundant resources, low cost and diverse material types. However, the huge volume change caused by the conversion reaction during cycling can lead to the pulverization of materials and rapid capacity decay. Common methods to improve the electrochemical performance of iron sulfide include: (1) designing unique nanostructures, especially multi-level structures, to shorten the electron / ion diffusion path and buffer the volume expansion during cycling; (2) combining with some carbonaceous materials to improve conductivity, suppress volume change and prevent polysulfide dissolution; (3) constructing heterostructures; (4) heteroatom doping is considered a simple and feasible method to improve the electrochemical performance of single metal sulfides. Inequivalent element doping will have different effects on the electrical properties of the donor. Doping atoms with more valence electrons will bring more free electrons, while doping atoms with fewer valence electrons will form more holes. Both of these different effects can improve the conductivity of the electrode material. Larger atomic doping also improves the lattice parameters to accommodate more sodium ions. In addition, some doping can alter the structure and morphology of the material.

[0004] Cation doping technology has been applied to some transition metal oxides used as anodes in lithium-ion batteries (LIBs), such as NiO and ZnO, which exhibit superior conductivity due to their complex chemical composition and the synergistic effect of multiple metals. Doping electroactive materials with anions to introduce intrinsic defects and modulate band structure has proven to be another feasible approach to improve reaction kinetics.

[0005] The rise of the high-entropy concept has sparked researchers' interest in the combination of various cation elements. Increasing the configurational entropy of a material enhances its stability, a phenomenon simply known as the high-entropy effect. It can stabilize crystal structures through entropy-driven cation mixing. However, introducing excessive amounts of inactive cations reduces capacity, further diminishing the benefits of high entropy. Therefore, a balance needs to be struck between high-entropy doping and high capacity, and the structure-activity relationship of high-entropy doping in improving electrochemical performance needs further investigation. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention prepares Fe7S8 co-doped with high-entropy cations and single anions as a negative electrode material for sodium-ion batteries using a simple ball milling-high-temperature sulfidation strategy. This significantly improves the capacity and cycle stability of the Fe7S8 material after high-entropy cation doping and single anion co-doping.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of this invention provides a high-entropy cation and anion co-doped Fe7S8 (HE-Fe7S) 8-x Se x The preparation method of ) includes the following steps:

[0009] Fe, Ni, Mo, Cr, W, Si, S, and Se powders were mixed and ball-milled, then placed in a tube furnace for high-temperature sulfidation to obtain HE-Fe7S. 8-x Se x .

[0010] Preferably, the molar ratio of Fe, Ni, Mo, Cr, W, and Si powders is 90:(1.5-2.5):(1.5-2.5):(1.5-2.5):(1.5-2.5):(1.5-2.5); more preferably, the molar ratio of Fe, Ni, Mo, Cr, W, and Si powders is 90:(1.8-2.2):(1.8-2.2):(1.8-2.2):(1.8-2.2):(1.8-2.2); and even more preferably, the molar ratio of Fe, Ni, Mo, Cr, W, and Si powders is 90:2:2:2:2:2.

[0011] Preferably, the ratio of the total molar number of Fe, Ni, Mo, Cr, W, and Si powders to the molar number of S and Se powders is 1:(0.8-1.2):(0.8-1.2); more preferably, the ratio of the total molar number of Fe, Ni, Mo, Cr, W, and Si powders to the molar number of S and Se powders is 1:(0.9-1.1):(0.9-1.1); even more preferably, the ratio of the total molar number of Fe, Ni, Mo, Cr, W, and Si powders to the molar number of S and Se powders is 1:1:1.

[0012] Preferably, the rotational speed of the ball mill is 1600-2000 r / min; more preferably, the rotational speed of the ball mill is 1700-1900 r / min; and even more preferably, the rotational speed of the ball mill is 1800 r / min.

[0013] Preferably, the ball milling time is 3-5 hours; more preferably, the ball milling time is 3.5-4.5 hours; and even more preferably, the ball milling time is 4 hours.

[0014] Preferably, the high-temperature vulcanization conditions are: heating to 550-650℃ at a heating rate of 3-7℃ / min and holding for 2.5-3.5h; more preferably, the high-temperature vulcanization conditions are: heating to 580-620℃ at a heating rate of 4-6℃ / min and holding for 2.8-3.2h; and even more preferably, the high-temperature vulcanization conditions are: heating to 600℃ at a heating rate of 5℃ / min and holding for 3h.

[0015] The second aspect of the present invention provides a HE-Fe7S 8-x Se x It was prepared by the method described above for preparing Fe7S8 co-doped with high-entropy cations and anions.

[0016] The third aspect of the present invention provides the aforementioned HE-Fe7S 8-x Se x Application in the preparation of anodes for sodium-ion batteries.

[0017] A fourth aspect of the present invention provides a sodium-ion battery negative electrode, wherein the surface of the sodium-ion battery negative electrode is loaded with the HE-Fe7S. 8-x Se x .

[0018] Preferably, the surface of the sodium-ion battery negative electrode is loaded with HE-Fe7S. 8-x Se x The loading capacity is 0.8-1.2 mg / cm³. 2 .

[0019] In some specific embodiments of the present invention, the method for preparing the sodium-ion battery negative electrode includes the following steps:

[0020] The HE-Fe7S 8-x Se x A slurry is prepared by mixing carbon black, polyvinylidene fluoride, and N-methylpyrrolidone, then coated onto copper foil, and dried to obtain an electrode sheet.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention employs high-entropy cation doping of iron-based sulfides with five elements to obtain more crystal defects and expose more active sites, thereby improving charge-discharge capacity. It also finely adjusts the coordination environment and electron distribution, and induces crystal defects (substitution, interstitial, vacancy, etc.) to optimize Na... + The migration path and energy barrier were improved, the interfacial electron transfer was improved, and the problem of slow kinetics was solved. On the basis of improving the charge and discharge capacity of Fe7S8 anode material by high-entropy cation doping, Se doping was further improved to increase the pseudocapacitance contribution rate and improve rate performance and cycle performance.

[0023] Multiple cations increase configuration entropy, which drives cation mixing and stabilizes the crystal structure. The hysteresis diffusion effect brought about by high entropy doping slows down particle aggregation, maintains the structural stability of the active material and the integrity of the electrode, and solves the problem of poor cycle stability.

[0024] A simple preparation method using solvent-free ball milling and high-temperature sulfidation improves material utilization. Furthermore, the raw material is a corresponding single-element powder, eliminating the tedious work of impurity removal, resulting in less pollution, higher material utilization, and reducing the complex process of heteroatom-doped iron-based sulfide synthesis, thus simplifying the synthesis route of high-performance sodium-ion anode materials.

[0025] Considering the abundant natural reserves and low cost of iron-based sulfides, using them as electrode materials makes industrialization easier, reduces production costs, and solves problems such as high production costs and long production times. Attached Figure Description

[0026] Figure 1 HE-Fe7S 8-x Se x Synthesis diagram;

[0027] Figure 2 Fe7S8, HE-Fe7S8, and HE-Fe7S prepared for the examples 8-x Se x X-ray diffraction pattern (XRD);

[0028] Figure 3(ac) represent Fe7S8, HE-Fe7S8, and HE-Fe7S prepared in the examples, respectively. 8-x Se x Scanning electron microscope (SEM); Figure 3 (d,e) represents HE-Fe7S 8-x Se x Transmission electron microscope (TEM) images at different magnifications; Figure 3 (fn) represents HE-Fe7S 8-x Se x Image showing the distribution of each element;

[0029] Figure 4 Fe7S8, HE-Fe7S8, and HE-Fe7S prepared for the examples 8-x Se x Rate performance and 1Ag -1 5A g -1 Cyclic performance at current density. Detailed Implementation

[0030] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0032] Example 1

[0033] S1: Mix 180mg Fe powder with 22836mg S powder (molar ratio 1:1), place in a vibratory ball mill, seal the ball mill jar under nitrogen, and ball mill at 1800r / min for 4 hours to achieve uniform mixing, fine particle refinement and solid solution.

[0034] S2: The obtained powder is placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen conditions and held for 3 hours for high-temperature sulfidation to obtain Fe7S8 single-phase powder.

[0035] Example 2

[0036] S1: Mix 180mg Fe powder, 4.21mg Ni powder, 6.86mg Mo powder, 3.71mg Cr powder, 13.14mg W powder, 2.00mg Si powder, and 228.6mg S powder (in a molar ratio of 90:2:2:2:2:2:200), place the mixture in a vibratory ball mill, seal the milling jar under nitrogen atmosphere, and ball mill at 1800 r / min for 4 hours to achieve uniform mixing, particle refinement, and solid solution.

[0037] S2: The obtained powder is placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen atmosphere and held for 3 hours for high-temperature sulfidation to obtain HE-Fe7S8 powder.

[0038] Example 3

[0039] S1: Mix 180mg Fe powder, 4.21mg Ni powder, 6.86mg Mo powder, 3.71mg Cr powder, 13.14mg W powder, 2.00mg Si powder, 228.6mg S powder and 282.0mg Se powder (molar ratio 90:2:2:2:2:2:100:100), place in a vibratory ball mill, seal the ball mill jar under nitrogen, and ball mill at 1800 r / min for 4 hours to achieve uniform mixing, fine particle size and solid solution.

[0040] S2: The obtained powder was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen atmosphere, and held at that temperature for 3 hours for high-temperature sulfidation to obtain HE-Fe7S. 8-x Se x powder.

[0041] The structures of the samples prepared in Examples 1-3 were characterized by X-ray diffraction to determine their composition and crystal structure, so as to study the effects of high-entropy cation doping and anion doping on the phase structure of the prepared iron sulfide. Figure 2The XRD pattern of Fe7S8 sample obtained by sulfurization of pure Fe powder shows that the four diffraction peaks at 29.96°, 33.92°, 44.0°, and 53.22° correspond to the four crystal planes (200), (203), (206), and (220) of hexagonal Fe7S8 (PDF#25-0411), indicating a single-phase structure. When Fe, Ni, Mo, Cr, W, Si powders and S powder are ball-milled and sulfurized at high temperature, the following results are obtained: In the HE-Fe7S8 sample, the diffraction peaks at 22.96°, 33.76°, 43.64° and 53.08° also correspond to the four crystal planes of hexagonal Fe7S8 (200), (203), (206) and (220), and the phase structure still exhibits a single-phase structure of Fe7S8. Furthermore, the diffraction peak positions corresponding to the Fe7S8 phase in the XRD patterns of the two samples mentioned above are slightly shifted to higher angles, indicating that the lattice parameters have been reduced. When Fe, Ni, Mo, Cr, W, and Si powders, along with S and Se powders, were ball-milled and subjected to high-temperature sulfurization to obtain samples (i.e., further Se doping), the diffraction angles of the characteristic peaks were 29.63°, 33.66°, 43.54°, and 52.64°, corresponding to the (200), (203), (206), and (220) crystal planes of the hexagonal Fe7S8 crystal system, exhibiting a single-phase structure of Fe7S8. Furthermore, the diffraction peak positions were significantly shifted to lower angles, confirming the successful incorporation of Se atoms, which have a larger atomic radius than S. The introduction of anionic Se doping did not affect the purity of the Fe7S8 material; on the contrary, the characteristic peaks of the material showed higher diffraction intensities after Se doping, indicating better crystallinity. The expansion of lattice parameters and interlayer spacing also implied defect growth, which is beneficial for Na… + The expansion of the diffusion path, thereby realizing Na + The rapid insertion and extraction of these atoms enhances the kinetics of sodium storage reactions. After the aforementioned high-entropy cation and anion doping, no obvious diffraction peaks or impurity peaks were detected in other metal sulfide or metal selenide crystal structures, indicating that these heteroatoms underwent only simple doping.

[0042] Further analysis of the XRD pattern revealed the lattice constant of the hexagonal Fe7S8 crystal. Favorable to Na + Transmission. HE-Fe7S 8-x Se x The lattice constant of the crystal is Compared to undoped Fe7S8 and HE-Fe7S8 crystals, both showed an increase in size, indicating that anion doping also plays a role in regulating the crystal structure.

[0043] Fe7S8, HE-Fe7S8, and HE-Fe7S were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 8-xSe x Morphological characteristics of Fe7S8, HE-Fe7S8, and HE-Fe7S8. 8-x Se x SEM such as Figure 3 As shown in (a), (b), and (c), Fe7S8, HE-Fe7S8, and HE-Fe7S 8-x Se x The particle morphology is non-uniform in size, ranging from 0.5 to 3 μm. With the doping of high-entropy cations, the particle size decreases; with the doping of anions, the agglomeration phenomenon is alleviated. These effects may be due to the hysteresis diffusion effect caused by high-entropy doping, which is beneficial to maintaining the structural stability of the active material and the integrity of the electrode. Figure 3 (d) and (e) are HE-Fe7S 8-x Se x TEM image, Figure 3 (f)-(n) in the equation represents HE-Fe7S 8-x Se x The mapping image, combined with the energy dispersive spectroscopy (EDS) mapping image ( Figure 3 (fn) further demonstrates the successful doping of Ni, Mo, Cr, W, Si, and Se. The five cations replace the Fe ion, while the Se ion replaces the S ion. The elements exhibit the same distribution region, indicating that they are uniformly distributed within the HE-Fe7S matrix. 8-x Se x middle.

[0044] Assembly of button half-cells with negative electrode material

[0045] The materials obtained in the above examples were mixed with superconducting carbon black and polyvinyl difluoroethylene (PVDF) in a weight ratio of 8:1:1 and dissolved in N-methylpyrrolidone (NMP). The resulting homogeneous slurry was then coated onto copper foil, which was dried in a vacuum oven at 60°C for 12 hours. The dried copper foil was then cut into electrode discs with a diameter of 12 cm, and the mass loading of the active material in the electrode discs was approximately 0.8–1.2 mg / cm². -2 All CR2032 button cells were assembled in an argon-filled glove box, using sodium sheet, glass fiber membrane, and NP005 (1.0M NaPF6 dissolved in diethylene glycol dimethyl ether solution) as the negative electrode, membrane, and electrolyte, respectively. For performance analysis, half-cells were assembled. Since metallic sodium has a lower potential than the material, the material was used as the positive electrode and metallic sodium as the negative electrode in the half-cell study. Charge-discharge tests were conducted on the Neware battery testing system (Neware BST76) in Shenzhen, China, with a voltage window of 0.01-3.0V.

[0046] Figure 4The magnification diagram of the material prepared for the example and 1Ag -1 5A g -1 Cyclic performance at current density, where, Figure 4 The upper middle section is a ratio chart. Figure 4 The graph on the bottom left shows the current density at 1 A / g. Figure 4 The graph on the bottom right shows the current density at 5 A / g. (For example...) Figure 4 As shown, HE-Fe7S 8-x Se x The highest capacity retention and best rate performance were observed at different rate expansions. Specifically, at 0.5 Ag... -1 The reversible specific capacity reaches 612.5 mAh g. -1 In 5Ag -1 The reversible specific capacity reaches 595.5 mAh g. -1 Even in 20A g -1 The reversible specific capacity is also 413 mAh g⁻¹. When the current density returns to 0.5 A g⁻¹... -1 At that time, the capacity recovered to 586.5mAhg -1 Such high capacity and excellent rate performance may be due to the abundant defects brought about by the co-doping of anions and cations, which provide more active sites for sodium storage and reduce Na+. + This is caused by the embedded energy barrier. HE-Fe7S 8-x Se x It not only has excellent rate performance but also excellent cycle performance. HE-Fe7S8 and HE-Fe7S 8-x Se x The performance of [the doped Fe7S8] is significantly better than that of undoped Fe7S8. Specifically, at 1 Å g... -1 HE-Fe7S under low current density charge-discharge cycles 8-x Se x The negative electrode still retains a reversible capacity of 655.9 mAh g after 334 charge-discharge cycles. -1 It outperforms many other similar Fe7S8 anode materials used in sodium-ion batteries. At 5Ag... -1 During high current density charge-discharge cycles, HE-Fe7S8 (353 cycles, 425.0 mAh g) -1 The Fe7S8 (133 cycles, 377.9 mAh g) outperforms the Fe7S8 (65.2%) in both capacity and cycle life (65.2%). -1 (84.5%), but the capacity retention rate was not ideal; while HE-Fe7S 8-x Se x Its cycle performance has been greatly improved in all aspects, and after 1858 charge-discharge cycles, the reversible capacity still reaches 534.87 mAh g. -1 At 0.5Ag-1 During charge and discharge, HE-Fe7S 8-x Se x The initial coulombic efficiency reached 79.73%, and the second cycle saw a rapid increase to 97.41%, indicating the formation of a stable SEI film during the first cycle and reducing subsequent interfacial side reactions. In subsequent charge-discharge cycles, the coulombic efficiency approached 100%, which may be partly attributed to the affinity of ether-based electrolytes for iron sulfide anode materials. Furthermore, both HED-Fe7S8 and HE-Fe7S... 8-x Se x , in 1A g -1 and 5Ag -1 During charge-discharge cycles, the capacity increases after a certain number of cycles. This may be due to the gradual activation of kinetics during each cycle, with sodium storage behavior gradually penetrating into the interior of the electrode material, thus providing higher capacity.

[0047] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. An application of high-entropy cation and anion co-doped Fe7S8 in the preparation of sodium-ion battery anodes, characterized in that, The preparation method of high-entropy cation and anion co-doped Fe7S8 includes the following steps: Fe, Ni, Mo, Cr, W, Si, S, and Se powders are mixed and ball-milled, then placed in a tube furnace for high-temperature sulfidation to obtain high-entropy cation and anion co-doped Fe7S8. The molar ratio of Fe, Ni, Mo, Cr, W, and Si powders is 90:(1.5-2.5):(1.5-2.5):(1.5-2.5):(1.5-2.5):(1.5-2.5), and the ratio of the total molar number of Fe, Ni, Mo, Cr, W, and Si powders to the molar number of S and Se powders is 1:(0.8-1.2):(0.8-1.2). The high-temperature sulfidation conditions are: heating to 550-650℃ at a heating rate of 3-7℃ / min and holding at that temperature for 2.5-3.5h.

2. The application according to claim 1, characterized in that, The ball mill rotates at a speed of 1600-2000 r / min.

3. The application according to claim 1, characterized in that, The ball milling time is 3-5 hours.

4. A sodium-ion battery negative electrode, characterized in that, The sodium-ion battery anode surface is loaded with high-entropy cation and anion co-doped Fe7S8 prepared by the method described in claim 1.

5. The sodium-ion battery negative electrode according to claim 4, characterized in that, The sodium-ion battery anode surface is loaded with 0.8-1.2 mg / cm³ of high-entropy cation and anion co-doped Fe7S8. 2 .

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