High-entropy sulfur selenide negative electrode material, preparation method thereof and application of high-entropy sulfur selenide negative electrode material in sodium-ion battery

Abstract

The invention discloses a high-entropy sulfur selenide negative electrode material, a preparation method thereof and application of the high-entropy sulfur selenide negative electrode material in a sodium-ion battery. The multi-element sulfur selenide negative electrode material with the high-entropy effect is synthesized in one step through a solvothermal method, and the chemical formula of the high-entropy negative electrode material is Mo < x > Sn < y > Sb Bi Co < c > S < d > S < e, 0 lt >, x is less than or equal to 1, 0lt; y is less than or equal to 0.05, 0lt; a is less than or equal to 0.05, 0lt; b is less than or equal to 0.05, 0lt; c is less than or equal to 0.05, 0lt; d < = 1, 0.05 < = e < = 0.15. The preparation method is relatively simple and convenient in process, good in controllability and capable of effectively promoting uniform mixing and reaction of various metal elements. Due to the unique high-entropy structure and sulfur-selenium composite anions, the obtained material shows excellent structural stability in the charge-discharge cycle process of a secondary battery (such as a sodium ion battery and a lithium ion battery), and is obviously superior to a corresponding binary or quaternary material, so that the material has long cycle life, high capacity retention ratio and stable comprehensive electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a high-entropy sulfoselenide negative electrode material, a preparation method thereof and application thereof in sodium ion batteries. BACKGROUND

[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 (1.02 Å) of sodium ions leads to easy collapse of the structure of the electrode material during charging and discharging. Traditional negative electrode materials such as hard carbon have limited capacity (<300 mAh / g), and alloy-based materials (such as Sn, Sb) face severe volume expansion (>300%), resulting in rapid degradation of cycle life. Sulfide negative electrodes (such as CuS, SnS) are of interest due to their high theoretical capacity (>500 mAh / g) and suitable working potential, but single-metal sulfides are prone to irreversible phase transitions during sodium storage, and the ion diffusion kinetics is slow.

[0003] Recent research attempts to buffer volume changes through multi-metal coordination (such as CuSbS2, SnSbS4), but binary or ternary systems still have problems of element segregation and lattice distortion. The concept of high-entropy materials (HEMs) provides a new way for electrode design: five or more main elements form high configurational entropy in the lattice, which suppresses element migration through "retarded diffusion effect" and "lattice distortion effect", and improves structural stability. However, existing high-entropy negative electrodes are mostly focused on oxides (such as (FeCoNiCrMn)3O4) or carbon-based composite materials, and research on sulfide high-entropy systems is still in the blank, which is due to two challenges of sulfide high-entropy: (1) The solubility product of multiple metal sulfides differs greatly, and co-precipitation synthesis easily leads to component deviation; (2) High-temperature solid-phase reaction easily causes sulfur volatilization, making it difficult to accurately control the stoichiometric ratio.

[0004] In addition, the semiconductor properties of pure sulfur anions (S 2- ) limit the electronic conductivity. The introduction of selenium (Se) to form a sulfur-selenium co-anion structure can adjust the energy band gap (such as the replacement of Se for S in CuSSe reduces the band gap from 2.0 eV to 1.4 eV), and improve the ion / electron dual conductivity, but existing sulfoselenide synthesis is mostly limited to simple binary systems (such as FeSSe, CoSSe), and multi-metal doping has not been combined with sulfur-selenium anion regulation, which cannot solve the structural stability and dynamic bottleneck at the same time.

[0005] Solvothermal method has been proven to be an effective means for preparing uniform nano-sulfide 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 comes to applying it to high-entropy sulfur selenides with five or more elements. 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 synergistic conduction advantage of sulfur and selenium, is the key approach to breaking through the bottlenecks of 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, which can synchronously solve the problems of structural pulverization, slow reaction kinetics and cycle life attenuation during sodium-ion insertion through the synergistic regulation of the high-entropy effect of five-element cations and sulfur-selenium mixed anions.

[0007] The present invention adopts a one-step solvothermal method. Molybdenum source, tin source, antimony source, bismuth source, cobalt source and sulfur source are mixed and dissolved in a reducing solvent and a reaction medium, and then the selenium source solution is dropped into the reaction system. Through low-temperature solvothermal crystallization, a five-element high-entropy sulfur selenide anode material with a single phase is directly synthesized. 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: On the one hand, the present invention proposes a preparation method for a high-entropy sulfur selenide anode material, which synthesizes Mo x Sn y Sb a Bi b Co c S d Se e High-entropy sulfur selenide anode material, 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; Weigh the molybdenum source, tin source, antimony source, bismuth source, cobalt source, sulfur source materials according to the proportion of each element in the chemical formula of the anode material 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, and finally obtain a powder product, which is the high-entropy sulfur selenide anode material (HESSe).

[0009] 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.

[0010] 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.

[0011] As control samples, the pentagonal high-entropy (selenium-free) material and the quaternary high-entropy material were prepared using the same method.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] Optionally, the vacuum drying process in the above preparation method is vacuum drying at 80-90℃ for 20-24 hours.

[0016] On the other hand, the present invention proposes a high-entropy sulfoselenide anode material prepared by the above-described preparation method.

[0017] 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.

[0018] The present invention has the following beneficial effects: 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.

[0019] 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

[0020] 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

[0021] 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.

[0022] Example 1

[0023] 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.

[0024] Example 2

[0025] 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.

[0026] Comparative Example 1: 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.

[0027] Comparative Example 2: 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.

[0028] Test example: 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 anode material, characterized in that, Includes the following steps: S1: The chemical formula of the high-entropy sulfoselenide anode 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; Weigh molybdenum source, tin source, antimony source, bismuth source, cobalt source, sulfur source according to the proportion of each element in the chemical formula of the anode material, and mix them in a solvent to form solution A; S2: Dissolve the selenium source in a solvent to form solution B; add solution B dropwise to solution A and stir thoroughly until homogeneous; transfer the mixed solution to a high-pressure reactor and react at a set temperature for several hours; after the reaction is complete, centrifuge to separate the precipitate, and wash thoroughly with anhydrous ethanol and deionized water in sequence; vacuum dry the washed powder to finally obtain the high-entropy sulfur selenide anode material.

2. The method for preparing a high-entropy sulfoselenide anode material according to claim 1, characterized in that, The molybdenum source is at least one of ammonium molybdate, sodium molybdate, molybdic acid, and molybdenum acetylacetonate. And / or, the tin source is at least one of stannous acetate, stannous oxalate, and stannous chloride; And / or, the antimony source is at least one of antimony acetate, antimony trichloride, and antimony pentachloride; And / or, the bismuth source is at least one of bismuth nitrate, bismuth acetate, and bismuth citrate; And / or, the cobalt source is at least one of cobalt acetate, cobalt oxalate, and cobalt chloride; And / or, the sulfur source is at least one of thioacetamide, sulfur powder, and thiourea.

3. The method for preparing a high-entropy sulfoselenide anode material according to claim 1, characterized in that, The solvent mentioned in step S1 is one or more of deionized water, ethanol, ethylene glycol, and methanol.

4. The method for preparing a high-entropy sulfoselenide anode material according to claim 1, characterized in that, The selenium source mentioned in step S2 is one or more of selenium dioxide, selenite, selenium powder, and selenourea, and the solvent in solution B is one or more of deionized water, ethanol, ethylene glycol, and methanol.

5. The method for preparing a high-entropy sulfoselenide anode material according to claim 1, characterized in that, In step S2, the reaction temperature of the mixed solution transferred to the high-pressure reactor is 120-200℃, and the reaction time is 8-24 h.

6. The method for preparing a high-entropy sulfoselenide anode material according to claim 1, characterized in that, The vacuum drying process in step S2 involves vacuum drying at 80-90℃ for 20-24 hours.

7. A high-entropy sulfoselenide anode material prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the high-entropy sulfoselenide anode material as described in claim 7 in the preparation of sodium-ion batteries, characterized in that, include: The material is mixed with binder and conductive agent in NMP solvent at a certain mass ratio to form a slurry, which is then coated onto the current collector to form an electrode sheet with an active material loading of 1-2.5 mg / cm². A coin cell of sodium ion battery is assembled with a polypropylene / polyethylene composite membrane as the battery separator and a sodium metal sheet as the counter electrode. The electrolyte is a 1M NaPF6 DME solution.

9. The application of the high-entropy sulfoselenide anode material as described in claim 8 in the preparation of sodium-ion batteries, characterized in that, The adhesive is PVDF, the conductive agent is Super P, and the mass ratio of the material, adhesive and conductive agent is (7-8):1:1.

Images