High-entropy sulfoselenide negative electrode material, preparation method thereof and application thereof in sodium ion battery

Abstract

This invention discloses a high-entropy sulfose-selenide anode material, its preparation method, and its application in sodium-ion batteries. A multi-component sulfose-selenide anode material exhibiting a high-entropy effect was synthesized in one step via a solvothermal method. The chemical formula of this high-entropy anode material is: Mo. x Sn y Sb a Bi b Co c S d Se e ,0

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a high-entropy sulfur selenide anode material, its preparation method, and its application in sodium-ion batteries. Background Technology

[0002] With the surge in demand for renewable energy storage, sodium-ion batteries have become an important supplement to lithium-ion batteries due to their abundant resources and low cost. However, the large ionic radius of sodium ions (1.02 Å) makes them prone to causing structural collapse of electrode materials during charge and discharge. Traditional anode materials such as hard carbon have limited capacity (<300 mAh / g), while alloy materials (such as Sn and Sb) face severe volume expansion (>300%), resulting in a sharp decline in cycle life. Sulfide anodes (such as CuS and SnS) have attracted attention due to their high theoretical capacity (>500 mAh / g) and suitable operating potential, but single-metal sulfides are prone to irreversible phase transitions during sodium storage, and their ion diffusion kinetics are slow.

[0003] Recent studies have attempted to buffer volume changes through multi-metal synergy (such as CuSbS2, SnSbS4), but element segregation and lattice distortion problems still exist in binary or ternary systems. The concept of high-entropy materials (HEMs) provides a new approach to electrode design: five or more principal elements form a high configurational entropy in the lattice, which inhibits element migration and improves structural stability through the "hysteresis diffusion effect" and "lattice distortion effect". However, existing high-entropy anodes are mostly concentrated in oxides (such as (FeCoNiCrMn)3O4) or carbon-based composite materials, and research on high-entropy sulfide systems is still blank. This is due to two major challenges in the high-entropy transformation of sulfides: (1) the solubility products of various metal sulfides are very different, and co-precipitation synthesis is prone to component deviation; (2) high-temperature solid-phase reactions are prone to sulfur volatilization, making it difficult to accurately control the stoichiometric ratio.

[0004] In addition, pure sulfur anions (S 2- The semiconductor properties of selenium limit its electronic conductivity. Introducing selenium (Se) to form a sulfose-selenium co-anion structure can adjust the band gap (e.g., replacing S with Se in CuSSe reduces the band gap from 2.0 eV to 1.4 eV), improving the dual conductivity of ions and electrons. However, the synthesis of existing sulfose-selenides is mostly limited to simple binary systems (e.g., FeSSe, CoSSe). Multi-metal doping and sulfose-selenium anion regulation have not yet been combined, making it impossible to simultaneously solve the bottlenecks of structural stability and kinetics.

[0005] The solvothermal method has been proven to be an effective means for preparing uniform nanosulfide materials. Its low-temperature liquid-phase environment (<200 °C) is conducive to the uniform nucleation of multiple elements. However, there is still a lack of systematic research when it is applied to quinary and higher high-entropy sulfur selenides. Although existing patented technologies have proposed the preparation of high-entropy oxide cathodes, there are few reports on high-entropy sulfur selenides in the anode field. Therefore, developing a high-entropy sulfur selenide anode material with precisely controllable composition, possessing both the high-entropy stabilization effect and the sulfur-selenium synergistic conduction advantage, is the key way to break through the bottlenecks of the energy density and cycle life of sodium-ion batteries. Summary of the Invention

[0006] The object of the present invention is to provide a high-entropy sulfur selenide sodium-ion battery anode material, its solvothermal preparation method and application. By synergistically regulating the high-entropy effect of quinary cations and sulfur-selenium mixed anions, the problems of structural pulverization, slow reaction kinetics, and cycle life attenuation during sodium-ion insertion are synchronously solved.

[0007] The present invention adopts a one-step solvothermal method. A molybdenum source, a tin source, an antimony source, a bismuth source, a cobalt source and a sulfur source are mixed and dissolved in a reducing solvent and a reaction medium, and then a selenium source solution is dropped into the reaction system. A quinary high-entropy sulfur selenide anode material with a single phase is directly synthesized through low-temperature solvothermal crystallization. This method avoids element segregation caused by high-temperature calcination and does not require the introduction of surfactants or secondary coating treatment.

[0008] The specific preparation steps are as follows:

[0009] On the one hand, the present invention proposes a preparation method for a high-entropy sulfur selenide anode material. A solvothermal method is used to synthesize a high-entropy sulfur selenide anode material of Mo x Sn y Sb a Bi b Co c S d Se e where 0 < x ≤ 1, 0 < y ≤ 0.05, 0 < a ≤ 0.05, 0 < b ≤ 0.05, 0 < c ≤ 0.05, 0 < d ≤ 1, 0.05 ≤ e ≤ 0.15; According to the proportion of each element in the chemical formula of the anode material, weigh molybdenum source, tin source, antimony source, bismuth source, cobalt source, sulfur source materials and dissolve them in a solvent to form solution A; then dissolve the selenium source in a solvent to form solution B; slowly drop solution B into solution A and continue stirring for 30 minutes. Subsequently, transfer the mixed solution to a high-pressure reaction kettle and react at a constant temperature for several hours. After the reaction is completed, centrifuge to separate the precipitate, and wash it six times with anhydrous ethanol and deionized water respectively. Vacuum dry the washed powder to finally obtain a powder product, namely the high-entropy sulfur selenide anode material (HESSe).

[0010] This invention selects five specific metallic elements—molybdenum (Mo), tin (Sn), antimony (Sb), bismuth (Bi), and cobalt (Co)—for high-entropy construction after multi-dimensional consideration. The reasons are as follows: First, from a thermodynamic perspective, the sulfides / selenides of these metals have similar crystal structures (such as layered or orthorhombic phases), readily forming homogeneous solid solutions, which is the structural basis for achieving the high-entropy effect. Second, from an electrochemical perspective, each element plays a specific role: the molybdenum matrix (such as MoS2) provides a stable layered framework and excellent electronic conductivity; tin and antimony are recognized high-capacity sodium alloying elements, contributing considerable theoretical specific capacity; bismuth also possesses high capacity characteristics, and its unique reaction mechanism helps buffer volume changes; the introduction of cobalt further modulates the electronic structure of the material, enhances intrinsic conductivity, and catalyzes conversion reaction kinetics. The core consideration behind this multi-component combination is that the "cocktail effect" and lattice distortion generated by the high entropy effect can effectively suppress the irreversible phase transition and particle pulverization of a single metal component during charging and discharging. By utilizing synergistic effects to achieve complementary advantages at the atomic level, the three major challenges of capacity, stability and conductivity can be solved simultaneously.

[0011] In the preparation process, the selenium source is prepared separately as solution B and then slowly added dropwise to the main metal salt solution A, rather than being directly mixed. This is mainly based on the precise control of reaction kinetics. The reduction reaction kinetics of selenium sources (such as SeO2) in solvothermal systems differ from those of sulfur sources, with differences in reduction potential and nucleation rate. If directly mixed, selenium atoms may undergo reduction and precipitation too early and too quickly, resulting in excessively high local concentrations, causing component segregation, and making it difficult to achieve a uniform, atomic-level distribution of sulfur (S) and selenium (Se) atoms in the final product lattice. The dropwise addition method used in this invention essentially creates a controllable, slow-release environment, allowing the selenium source to participate in the crystal nucleus growth process gradually and smoothly. This ensures the uniform, atomic-level distribution of sulfur anions (S... 2- ) and selenium anion (Se 2- These atoms can be uniformly embedded into the forming pentagonal metal cation lattice, ultimately forming a sulfur-selenium composite anion structure with precise and controllable stoichiometry. This structure not only improves the electronic conductivity of the material by adjusting the band gap, but also utilizes the larger ionic radius and polarizability of Se atoms to broaden the sodium ion migration channels and significantly optimize sodium ion diffusion kinetics.

[0012] As control samples, the pentagonal high-entropy (selenium-free) material and the quaternary high-entropy material were prepared using the same method.

[0013] Optionally, the solvent in solution A or solution B in the above preparation method is one or more of deionized water, ethanol, ethylene glycol, and methanol.

[0014] Optionally, the molybdenum source in the above preparation method is at least one of ammonium molybdate, sodium molybdate, molybdic acid, and molybdenum acetylacetonate; the tin source includes at least one of stannous acetate, stannous oxalate, and stannous chloride; the antimony source includes at least one of antimony acetate, antimony trichloride, and antimony pentachloride; the bismuth source includes at least one of bismuth nitrate, bismuth acetate, and bismuth citrate; the cobalt source includes at least one of cobalt acetate, cobalt oxalate, and cobalt chloride; and the sulfur source includes at least one of thioacetamide, sulfur powder, and thiourea.

[0015] Optionally, in the above preparation method, the reaction temperature for transferring the mixed solution to the high-pressure reactor is 120-200℃, and the reaction time is 8-24 h.

[0016] Optionally, the vacuum drying process in the above preparation method is vacuum drying at 80-90℃ for 20-24 hours.

[0017] On the other hand, the present invention proposes a high-entropy sulfoselenide anode material prepared by the above-described preparation method.

[0018] Thirdly, this invention also provides the application of the aforementioned high-entropy sulfur-selenide anode material in sodium-ion batteries; wherein, the method of assembling a sodium-ion battery using the high-entropy anode material is a conventional method in the art, taking the assembly of a coin cell as an example, the specific steps are as follows: the anode material of this patent, polyvinylidene fluoride (PVDF), and Super P are mixed evenly in N-methylpyrrolidone (NMP) solvent at a mass ratio of (7-8):1:1 to prepare a slurry. The slurry is coated onto an aluminum foil current collector to prepare an electrode sheet, with a positive electrode active material loading of 1-2.5 mg / cm³. 2 A coin cell sodium-ion battery is assembled using a polypropylene / polyethylene composite membrane as the battery separator and a sodium metal sheet as the counter electrode, together with the separator and the aforementioned electrode sheet. The electrolyte is a 1M NaPF6 solution with 1,2-dimethoxyethane (DME-100%) as the solvent. This application fully leverages the high-entropy stabilizing effect of the materials and the synergistic advantages of sulfur and selenium anions, enabling the battery to possess high capacity, excellent rate performance, and long cycle life.

[0019] The present invention has the following beneficial effects:

[0020] This invention utilizes the high-entropy synergistic construction of five metal cations—molybdenum, tin, antimony, bismuth, and cobalt—to form a material with strong lattice distortion solid solution, significantly improving the crystal structure's tolerance to repeated sodium ion insertion / extraction. This unique design effectively dissipates stress accumulation during charge and discharge processes, fundamentally suppressing volume deformation and particle pulverization of the electrode material, achieving cycle durability far exceeding that of traditional sulfides, and ensuring the structural integrity of the electrode during long-term deep cycling.

[0021] This invention innovatively introduces a sulfur-selenium mixed anionic group, leveraging the orbital extension and high electron delocalization characteristics of selenium atoms to significantly optimize the electronic band structure and interfacial ion migration dynamics of the material. This design simultaneously enhances electron conduction efficiency and sodium ion diffusion rate, breaking through the charge transport bottleneck of conventional sulfide anodes. It endows the material with high-rate charge-discharge response while maintaining high specific capacity, providing a key electrode material solution for fast-charging sodium-ion batteries. Attached Figure Description

[0022] Figure 1 Comparative images show the long-cycle performance of coin cells made from the negative electrode materials obtained in Examples 1, 2, 1, and 2 of this invention at a current density of 1000 mA / g. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0024] Example 1

[0025] 0.7 g of sodium molybdate, 0.02 g of stannous acetate (II), 0.02 g of antimony acetate, 0.04 g of bismuth nitrate, 0.02 g of cobalt acetate, and 1.2 g of thiourea were mixed in 50 mL of ethanol (solution A). Separately, 0.04 g of selenium dioxide was mixed with 30 mL of ethanol to form solution B. After magnetic stirring for half an hour, solution B was slowly added dropwise to beaker A, and stirring continued for another half hour. The mixture was then transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 200 °C for 12 hours. After the reaction was complete, the precipitate was separated by centrifugation and washed six times each with anhydrous ethanol and deionized water. The final product was a powder.

[0026] Example 2

[0027] This embodiment provides another formulation of a pentagonal high-entropy sulfur-selenide anode material to demonstrate the universality of the invention within the composition window. 0.8 g of sodium molybdate, 0.02 g of stannous oxalate, 0.03 g of antimony trichloride, 0.02 g of bismuth citrate, 0.03 g of cobalt chloride, and 1.1 g of thioacetamide were weighed and dissolved together in 50 mL of ethylene glycol, and the solution was magnetically stirred to form a homogeneous solution A. Separately, 0.08 g of selenium powder was dissolved in 30 mL of ethylene glycol to form solution B. Solution B was slowly added dropwise to solution A under continuous stirring, and stirring was continued for 30 minutes to ensure sufficient pre-reaction. Subsequently, the mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at a mild temperature of 160°C for 18 hours. After the reaction, the precipitate was collected by centrifugation and washed thoroughly several times with anhydrous ethanol and deionized water. Finally, the obtained product was treated in a vacuum drying oven at 85°C for 22 hours to obtain a black powdery high-entropy sulfur selenide material.

[0028] Comparative Example 1:

[0029] To illustrate the advantages of introducing selenium into a pentagonal high-entropy system, a selenium-free pentagonal sulfide was prepared in this comparative example. 0.7 g of sodium molybdate, 0.02 g of stannous acetate, 0.02 g of antimony acetate, 0.04 g of bismuth nitrate, 0.02 g of cobalt acetate, and 1.2 g of thiourea were mixed in 80 mL of ethanol. After magnetic stirring for half an hour, the solution was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and reacted at 200 °C for 12 hours. After the reaction, the precipitate was separated by centrifugation and washed six times each with anhydrous ethanol and deionized water. The final product was a powder.

[0030] Comparative Example 2:

[0031] To illustrate the advantages of a pentagonal high-entropy system compared to a quaternary system, a cobalt-free quaternary sulfur-selenide was prepared in this comparative study. 0.7 g of sodium molybdate, 0.02 g of stannous acetate, 0.02 g of antimony acetate, 0.04 g of bismuth nitrate, and 1.2 g of thiourea were weighed and mixed in 50 mL of ethanol. After magnetic stirring for half an hour, solution A was formed. Separately, 0.08 g of selenium powder was dissolved in 30 mL of ethylene glycol to form solution B. Solution B was slowly added dropwise to solution A under continuous stirring, and stirring was continued for 30 minutes to ensure sufficient pre-reaction. Subsequently, the mixed solution was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and reacted at a mild temperature of 160 °C for 18 hours. After the reaction, the precipitate was collected by centrifugation and washed thoroughly several times with anhydrous ethanol and deionized water. Finally, the obtained product was treated in a vacuum drying oven at 85 °C for 22 hours to obtain a black powdery quaternary high-entropy sulfur-selenide material.

[0032] Test example:

[0033] The high-entropy negative electrode materials obtained in Examples 1 and 2, and Comparative Examples 1 and 2, were respectively assembled into coin cells. The specific assembly method was as follows: the active material, PVDF, and SuperP were mixed uniformly in NMP solvent at a mass ratio of 8:1:1 to prepare a slurry. The slurry was then coated onto a copper foil current collector to prepare the electrode sheet. The positive electrode active material loading was 2 mg / cm³. 2 A coin cell sodium-ion battery was assembled using a polypropylene / polyethylene composite membrane as the battery separator and a sodium metal sheet as the negative electrode. The electrolyte was a 1M NaPF6 solution with DME as the solvent. The battery was connected to a Xinwei system for electrical performance testing. The test voltage range was 0.01-3.0V, and the cycling curves for Examples 1 and 2 and Comparative Examples 1 and 2 were obtained. Figure 1 As can be seen from the figure, at a current density of 1000 mA / g, due to the unique structure of the high-entropy material, the material in Example 1 retains a capacity of 374 mAh / g after 40 cycles, while the material in Example 2 retains a capacity of 362 mAh / g. The difference in capacity between the two is small, and the capacity retention rate is close to 100%. In contrast, at the same current density and after 40 cycles, the capacity of the material in Comparative Example 1 has decreased to 337 mAh / g, with a capacity retention rate of 90%, while the initial capacity of the material in Comparative Example 2 is only 350 mAh / g, with a capacity retention rate of 93%. Both of these materials have worse initial capacity and capacity retention rates than the materials in the examples.

[0034] The fundamental reason for this phenomenon lies in the successful construction of a dual synergistic stabilization mechanism of a "high-entropy cation framework" and a "sulfur-selenium composite anion" in the embodiments of this invention. On the one hand, the high configurational entropy formed by the five main elements Mo, Sn, Sb, Bi, and Co in the crystal lattice generates a strong "hysteresis diffusion effect," which greatly restricts the migration and rearrangement of metal atoms during the repeated insertion and extraction of sodium ions. This acts like a robust alloy framework, effectively buffering phase transformation stress and fundamentally inhibiting particle pulverization. On the other hand, the design of the sulfur (S) and selenium (Se) composite anion plays a crucial role: the larger ionic radius of selenium atoms helps to moderately expand the interlayer spacing, providing a wider diffusion channel for sodium ions; simultaneously, the introduction of selenium significantly optimizes the electronic structure of the material, improving intrinsic electronic conductivity and ensuring efficient and reversible electrochemical reactions even at high rates. The synergistic effect of these two elements jointly guarantees the structural integrity and reaction kinetics of the electrode material during long-term cycling.

[0035] In contrast, Comparative Example 1 (a selenium-free pentagonal high-entropy sulfide) exhibited a capacity decay to 337 mAh / g after 40 cycles, with a retention rate of only 90%. This performance gap is primarily attributed to the absence of selenium. Although its pentagonal cation framework provides some high-entropy stability, the pure sulfur anions result in low intrinsic electronic conductivity and relatively small interlayer spacing, increasing resistance to sodium ion migration and enhancing reaction polarization. This kinetic disadvantage accumulates gradually during cycling, leading to greater internal stress and irreversible side reactions, ultimately manifesting as faster capacity decay. This comparison strongly demonstrates that the introduction of a selenium source is indispensable for optimizing reaction kinetics and achieving ultra-high cycling stability.

[0036] Comparative Example 2 (cobalt-free quaternary sulfoselenide) showed inferior initial capacity (350 mAh / g) and capacity retention after 40 cycles (93%) compared to the example, highlighting the advantage of the pentagonal high-entropy system over the quaternary system. The absence of cobalt directly led to a decrease in the system's configurational entropy, weakening the lattice anchoring effect brought about by the high-entropy effect, thus reducing the material's ability to resist volume changes and elemental segregation during cycling. This indicates that even with the introduction of selenium anions, the insufficient high-entropy of the cations still becomes a performance bottleneck, preventing the achievement of the ultimate stability provided by the pentagonal system.

[0037] In summary, the stark contrast between Examples 1 and 2 and Comparative Examples 1 and 2 collectively confirms a core conclusion: this invention successfully achieves a balance between structural stability and kinetic optimization through the precise coupling of the "high-entropy effect of the five-membered cation" and the "sulfur-selenium composite anion." The absence of either aspect would lead to a significant decrease in electrochemical performance.

Claims

1. A method for preparing a high-entropy sulfoselenide negative electrode material, characterized in that, Comprising the following steps: S1: The chemical formula of the high-entropy sulfoselenide negative electrode material is: Mo x Sn y Sb a Bi b Co c S d Se e , 0<x≤1, 0<y≤0.05, 0<a≤0.05, 0<b≤0.05, 0<c≤0.05, 0<d≤1, 0.05≤e≤0.15; according to the proportion of each element in the chemical formula of the negative electrode material, a molybdenum source, a tin source, an antimony source, a bismuth source, a cobalt source, and a sulfur source are weighed and mixed in a solvent to form a solution A; S2: Dissolve the selenium source in a solvent to form solution B; add the B solution dropwise to solution A with sufficient stirring to mix uniformly, transfer the mixed solution to a high-pressure reaction kettle, react at a set temperature for several hours, after the reaction is complete, centrifuge the precipitate, and sequentially wash with anhydrous ethanol and deionized water; vacuum dry the washed powder to obtain the high-entropy sulfoselenide negative electrode material; The molybdenum source is at least one of ammonium molybdate, sodium molybdate, molybdic acid, and molybdenum acetylacetone; the selenium source is one or more of selenium dioxide, selenite, selenium powder, and selenium urea; The tin source is at least one of stannous acetate, stannous oxalate, and stannous chloride; The antimony source is at least one of antimony acetate, antimony trichloride, and antimony pentachloride; The bismuth source is at least one of bismuth nitrate, bismuth acetate, and bismuth citrate; The cobalt source is at least one of cobalt acetate, cobalt oxalate, and cobalt chloride; The sulfur source is at least one of thioacetamide, sulfur powder, and thiourea.

2. The preparation method of the high-entropy sulfoselenide negative electrode material according to claim 1, characterized in that, The solvent in step S1 is one or more of deionized water, ethanol, ethylene glycol, and methanol.

3. The preparation method of the high-entropy sulfoselenide negative electrode material according to claim 1, characterized in that, In step S2, the solvent in solution B is one or more of deionized water, ethanol, ethylene glycol, and methanol.

4. The preparation method of the high-entropy sulfoselenide negative electrode material according to claim 1, characterized in that, The reaction temperature when the mixed solution in step S2 is transferred to the high-pressure reaction kettle is 120-200°C, and the reaction time is 8-24 h.

5. The preparation method of the high-entropy sulfoselenide negative electrode material according to claim 1, characterized in that, The vacuum drying process in step S2 is vacuum drying at 80-90°C for 20-24 h.

6. A high-entropy sulfoselenide negative electrode material prepared by the preparation method of any one of claims 1 to 5.

7. The use of the high-entropy sulfoselenide negative material according to claim 6 in the preparation of sodium-ion batteries, characterized in that, Comprising: Mix the material with a binder and a conductive agent in a certain mass ratio in NMP solvent to form a slurry, coat the slurry on a current collector to form an electrode sheet, and the active material loading is 1-2.5 mg / cm2; use a polypropylene / polyethylene composite film as a battery separator, a sodium metal sheet as a counter electrode, assemble a sodium ion battery button cell, and the electrolyte is a 1M NaPF6 DME solution.

8. Use of the high-entropy sulpho-selenide negative material according to claim 7 for the preparation of a sodium-ion battery, characterized in that, The binder is PVDF, the conductive agent is Super P, and the mass ratio of the material, the binder, and the conductive agent is (7-8):1:1.

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