A negative electrode material, its preparation method, and a sodium-ion battery

Abstract

This application provides an anode material, its preparation method, and a sodium-ion battery, belonging to the field of anode material manufacturing technology. The anode material includes a carbon nanotube substrate with a three-dimensional network structure and high-entropy metal sulfide particles. The high-entropy metal sulfide particles are loaded on the surface of the carbon nanotubes in the carbon nanotube substrate and / or the inner wall of the carbon nanotube cavities. The high-entropy metal sulfide particles are a single-phase solid solution formed by at least five equimolar amounts of metal elements and sulfur. This anode material is synergistically constructed from the single-phase solid solution of high-entropy metal sulfide and the carbon nanotube substrate with a three-dimensional conductive network. This results in a cathode material with superior conductivity and sodium-ion transport rate, and effectively mitigates the volume expansion of the high-entropy metal sulfide during charge and discharge, enabling the corresponding battery to possess superior capacity, rate performance, and cycle stability.

Description

Technical Field

[0001] This application relates to the field of negative electrode material manufacturing technology, and more specifically, to a negative electrode material, its preparation method, and a sodium-ion battery. Background Technology

[0002] In the prior art, compared with traditional single metal sulfides or binary metal sulfides, high-entropy metal sulfides can optimize the electronic structure and regulate the bonding strength of metal-sulfur bonds through multi-metal synergy. At the same time, the rich elemental composition provides a large number of active sites and defect structures, which is beneficial to improving the storage capacity and reaction kinetics of sodium ions.

[0003] However, the application of high-entropy metal sulfides in sodium-ion batteries still faces significant challenges: First, while the introduction of multi-metal components can modulate the electronic structure, the overall intrinsic conductivity of the material remains low, limiting the electron transport rate. Second, the large radius of sodium ions easily causes severe volume expansion of high-entropy metal sulfides during repeated insertion / extraction, leading to electrode material pulverization and structural collapse, resulting in poor cycle stability of the corresponding battery. Third, high-entropy metal sulfide nanoparticles are prone to agglomeration during preparation, making uniform dispersion difficult and affecting the rate performance and capacity of the corresponding electrode. Therefore, it is urgent to address the aforementioned problems in the application of high-entropy metal sulfides in sodium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide an anode material, its preparation method, and a sodium-ion battery. The anode material is synergistically constructed from a high-entropy metal sulfide and a carbon nanotube substrate with a three-dimensional conductive network, which enables the anode material to have excellent conductivity and sodium ion transport rate, and can also effectively alleviate the volume expansion of the high-entropy metal sulfide during charge and discharge. At the same time, the high-entropy metal sulfide is a single-phase solid solution, so that the corresponding battery has excellent capacity, rate performance, and cycle stability.

[0005] The embodiments of this application are implemented as follows: In a first aspect, embodiments of this application provide a negative electrode material, including a carbon nanotube substrate with a three-dimensional network structure and high-entropy metal sulfide particles. The high-entropy metal sulfide particles are loaded on the surface of the carbon nanotubes in the carbon nanotube substrate and / or the inner wall of the cavity of the carbon nanotubes. The high-entropy metal sulfide particles are made of a single-phase solid solution formed by at least five equimolar amounts of metal elements and sulfur elements.

[0006] In the above technical solution, the negative electrode material is synergistically constructed from high-entropy metal sulfides and a carbon nanotube substrate with a three-dimensional conductive network. On one hand, the high-entropy metal sulfide particles, relying on the carbon nanotube substrate with a three-dimensional conductive network (carbon nanotubes possess excellent electronic conductivity and mechanical flexibility), enable the negative electrode material to exhibit superior conductivity and sodium ion transport rate. Furthermore, its mechanical flexibility effectively mitigates the volume expansion of the high-entropy metal sulfide particles during charging and discharging, reducing the probability of electrode structure pulverization and collapse. On the other hand, the high-entropy metal sulfide particles are a single-phase solid solution formed by at least five equimolar amounts of metal elements and sulfur. This specific type of high-entropy metal sulfide can... The electrochemical performance of the material is optimized from multiple aspects, including high-entropy effect, lattice distortion effect, and hysteresis diffusion effect: (1) The synergistic effect of the multi-metal components regulates the bonding strength of the metal-sulfur bond, optimizes the electronic structure, and improves the intrinsic electronic conductivity of the material; (2) The high-entropy structure introduces abundant defect sites and lattice distortion, providing more storage sites and diffusion channels for sodium ions, significantly improving the sodium storage capacity; (3) The synergistic catalytic effect among the multi-metal elements reduces the reaction energy barrier of sodium ions in the insertion / extraction process and accelerates the reaction kinetics; (4) The high-entropy components can effectively suppress phase transitions and element segregation during the charge and discharge process, maintain the structural stability of the material, and thus obtain excellent cycle life. Through the combined effect of these two aspects, the corresponding battery can have relatively excellent capacity, rate performance, and cycle stability.

[0007] In some alternative implementations, the carbon nanotube substrate has a diameter of 10 nm to 50 nm and a length of 1 μm to 20 μm for individual carbon nanotubes, and a particle size of 10 nm to 200 nm for individual high-entropy metal sulfide particles.

[0008] In the above technical solution, the diameter and length of a single carbon nanotube are simultaneously limited within the aforementioned range, so that the carbon nanotube has a more suitable size, which helps to construct a continuous three-dimensional conductive network and can provide sufficient loading sites for high-entropy metal sulfide particles. On this basis, the particle size of a single high-entropy metal sulfide particle is simultaneously limited within the aforementioned range, which enables the high-entropy metal sulfide particles to be stably loaded on the carbon nanotube and to bind the two tightly. At the same time, it also enables the high-entropy metal sulfide particles to have a larger specific surface area to provide more active sites, thereby effectively improving electron transport efficiency.

[0009] In some alternative implementations, the metallic element is selected from at least five of the following: cobalt, iron, nickel, copper, zinc, manganese, chromium, manganese, molybdenum, tin, antimony, and bismuth.

[0010] In the above technical solutions, the types of metal elements are limited to the above range, and the corresponding high-entropy metal sulfides can produce a better synergistic effect, thereby better optimizing the electrochemical performance of the negative electrode material; at the same time, the embodiments of this application are applicable to a wide variety of metal elements, which can provide a wide range of feasible solutions, thereby facilitating the promotion and application of the technical solutions provided by the embodiments of this application.

[0011] Secondly, embodiments of this application provide a method for preparing the negative electrode material as provided in the first aspect embodiment, comprising the following steps: uniformly dispersing metal salts of various metal elements, carbon nanotubes, and organic ligands in a first solvent, wherein the molar amounts of various metal elements are all the same, to obtain a precursor dispersion; subjecting the precursor dispersion to a first solvothermal reaction under stirring conditions, wherein the reaction temperature is 110℃~190℃ and the reaction time is 10 h~24 h; performing a first solid-liquid separation after the reaction to obtain a carbon nanotube substrate loaded with a high-entropy metal precursor; uniformly dispersing the carbon nanotube substrate loaded with the high-entropy metal precursor and a first sulfur source in a second solvent and subjecting it to a second solvothermal reaction under stirring conditions, wherein the reaction temperature is 130℃~200℃ and the reaction time is 10 h~24 h. After the reaction is completed, a second solid-liquid separation is performed to obtain a carbon nanotube substrate loaded with a high-entropy metal sulfide precursor. The carbon nanotube substrate loaded with the high-entropy metal sulfide precursor and a second sulfur source are mixed and heat-treated. The treatment temperature is 500℃~800℃, the treatment time is 1 h~5 h, and the heating rate is 1℃ / min~10℃ / min to obtain the anode material.

[0012] In the above technical solution, the first solvothermal reaction is carried out under the above conditions, which enables the organic ligands and various metal ions to fully coordinate and form a high-entropy metal precursor, which grows in situ and is uniformly distributed on the surface of the carbon nanotube and the inner wall of the cavity (the carbon nanotube will simultaneously achieve self-assembly through winding and other methods during the reaction to form a carbon nanotube substrate with a three-dimensional network structure), so as to obtain a carbon nanotube substrate loaded with a high-entropy metal precursor; the second solvothermal reaction is carried out under the above conditions, which enables the metal in the high-entropy metal precursor to be fully sulfidated under the action of the first sulfur source and form a metal sulfide, so as to form a carbon nanotube substrate loaded with a high-entropy metal sulfide precursor; the heat treatment is carried out under the above reaction conditions, which enables the metal element to be further sulfidated and the metal sulfide to be fully crystallized, so as to form a single-phase solid solution of high-entropy metal sulfide particles, and also makes the formed high-entropy metal sulfide particles have the advantages of uniform particle size and suitable size, good structural stability and not easy to agglomerate. The above process can ultimately produce an anode material that is synergistically constructed from a high-entropy metal sulfide of a single-phase solid solution and a carbon nanotube substrate with a three-dimensional conductive network.

[0013] In some alternative embodiments, the ratio of the total mass of the metal salts of various metal elements to the mass of carbon nanotubes in the precursor dispersion is (5~15):1; or / and the ratio of the total mass of the metal salts of various metal elements to the mass of organic ligands in the precursor dispersion is 1:(0.5~2).

[0014] In the above technical solution, limiting the ratio of the total mass of metal salts of various metal elements in the precursor dispersion to the mass of carbon nanotubes within the aforementioned range enables the high-entropy metal sulfide particles to be uniformly dispersed on the carbon nanotubes and have a suitable loading. Limiting the ratio of the total mass of metal salts of various metal elements in the precursor dispersion to the mass of organic ligands within the aforementioned range enables the organic ligands and various metal elements to coordinate more fully and thoroughly to form a high-entropy metal precursor. This ensures that the molar ratio of various metal elements in the high-entropy metal precursor remains highly consistent with the feed ratio, which in turn helps to subsequently prepare high-entropy metal sulfide particles in a single-phase solid solution.

[0015] In some alternative embodiments, the reaction temperature in the first solvothermal reaction is 120°C to 180°C and the reaction time is 12 h to 20 h.

[0016] In the above technical solution, the temperature and duration of the first solvothermal reaction are further limited within the above range, which enables the organic ligands and various metal ions to coordinate more fully and thoroughly to form a high-entropy metal precursor. At the same time, it also enables the formed high-entropy metal precursor to be more uniformly dispersed and more tightly bound on the carbon nanotubes.

[0017] In some alternative embodiments, the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal precursor to the mass of the first sulfur source is 1:(1.5~3); or / and, in the second solvothermal reaction, the reaction temperature is 140℃~180℃ and the reaction time is 12 h~20 h.

[0018] In the above technical solution, limiting the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal precursor to the mass of the first sulfur source within the above range enables the metal in the high-entropy metal precursor to be more fully and thoroughly sulfided and form metal sulfides under the action of the first sulfur source; further limiting the temperature and duration of the second solvothermal reaction within the above range enables the metal in the high-entropy metal precursor to be more fully and thoroughly sulfided and form metal sulfides under the action of the first sulfur source.

[0019] In some alternative embodiments, the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal sulfide precursor to the mass of the second sulfur source is 1:(2~5); or / and, in the heat treatment step, the reaction temperature is 500℃~700℃, the reaction time is 1 h~5 h, and the heating rate is 4℃ / min~8℃ / min.

[0020] In the above technical solution, limiting the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal sulfide precursor to the mass of the second sulfur source within the aforementioned range can more effectively compensate for sulfur loss at high temperatures, so as to better maintain the stoichiometric ratio of various elements in the metal sulfide precursor, and thus better facilitate the preparation of high-entropy metal sulfide particles in a single-phase solid solution after crystallization. Further limiting the temperature, duration and heating rate of the heat treatment within the aforementioned range can make the metal elements more fully and thoroughly sulfidated and the metal sulfide more fully and thoroughly crystallized. It also makes the formed high-entropy metal sulfide particles have the advantages of more uniform particle size and more suitable size, better structural stability and more dispersion.

[0021] In some alternative embodiments, the organic ligand is selected from at least one of glyceric acid, citric acid, ethylenediaminetetraacetic acid, and tartaric acid; and / or the first solvent and the second solvent are independently selected from at least one of isopropanol, ethanol, methanol, and ethylene glycol; and / or the first sulfur source and the second sulfur source are independently selected from at least one of thioacetamide, thiourea, and sulfur powder.

[0022] In the above technical solutions, the selection of the aforementioned organic ligands facilitates the rapid coordination of various metal elements to form high-entropy metal precursors and their stable loading onto carbon nanotubes; the selection of the aforementioned solvents enables efficient dispersion and uniform mixing of various components, facilitating efficient and thorough reaction at each stage, and ultimately contributing to the preparation of high-entropy metal sulfide particles in a single-phase solid solution; the selection of the aforementioned sulfur source enables efficient and thorough sulfidation of metal elements, further contributing to the final preparation of high-entropy metal sulfide particles in a single-phase solid solution. Furthermore, the embodiments of this application offer a wide variety of applicable organic ligands, solvents, and sulfur sources, providing numerous feasible implementation schemes, thus facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0023] Thirdly, embodiments of this application provide a sodium-ion battery, wherein the negative electrode of the sodium-ion battery contains the negative electrode material provided in the first aspect embodiment.

[0024] In the above technical solution, the negative electrode of the sodium-ion battery contains the negative electrode material provided in the first aspect embodiment. Since the negative electrode material is synergistically constructed from a high-entropy metal sulfide in a single-phase solid solution and a carbon nanotube substrate with a three-dimensional conductive network, the negative electrode material has excellent conductivity and sodium ion transport rate, and can also effectively alleviate the volume expansion of the high-entropy metal sulfide during charging and discharging. At the same time, the high-entropy metal sulfide is a single-phase solid solution (this type of high-entropy metal sulfide can optimize the electrochemical performance of the material from multiple levels such as high-entropy effect, lattice distortion effect and hysteresis diffusion effect, and also has the synergistic coupling of four energy storage mechanisms: intercalation reaction, conversion reaction, alloying reaction and space charge storage), so that the sodium-ion battery has both excellent capacity, rate performance and cycle stability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A process flow diagram of a method for preparing a negative electrode material provided in an embodiment of this application; Figure 2 The image shows the XRD pattern of the negative electrode material prepared in Example 1 of this application. Figure 3 Here is a high-resolution SEM image of the negative electrode material prepared in Example 1 of this application; Figure 4 This is a TEM image of the negative electrode material prepared in Example 1 of this application; Figure 5 This is a high-resolution TEM image of the negative electrode material prepared in Example 1 of this application; Figure 6 This is a SEM image of the negative electrode material prepared in Example 2 of this application; Figure 7 This is a SEM image of the negative electrode material prepared in Example 3 of this application; Figure 8 This is a SEM image of the negative electrode material prepared in Example 4 of this application; Figure 9 This is a SEM image of the negative electrode material prepared in Example 5 of this application; Figure 10 The image shows the XRD pattern of the negative electrode material prepared in Comparative Example 1 of this application. Figure 11 The XRD pattern of the negative electrode material prepared in Comparative Example 2 of this application is shown. Figure 12TEM image of the negative electrode material prepared in Comparative Example 3 of this application; Figure 13 The image shows the XRD pattern of the negative electrode material prepared in Comparative Example 4 of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0028] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0029] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0030] The following describes in detail an example of a negative electrode material, its preparation method, and a sodium-ion battery according to embodiments of this application.

[0031] In a first aspect, embodiments of this application provide a negative electrode material, including a carbon nanotube substrate with a three-dimensional network structure and high-entropy metal sulfide particles. The high-entropy metal sulfide particles are loaded on the surface of the carbon nanotubes in the carbon nanotube substrate and / or the inner wall of the cavity of the carbon nanotubes. The high-entropy metal sulfide particles are made of a single-phase solid solution formed by at least five equimolar amounts of metal elements and sulfur elements.

[0032] It should be noted that "single-phase solid solution" refers to a high-entropy metal sulfide particle whose XRD pattern shows that all diffraction peaks can be indexed to the same crystal structure, and no diffraction peaks belonging to other phases or impurities are observed; moreover, the single-phase solid solution characteristic is a prerequisite for high-entropy metal sulfides to exhibit excellent performance.

[0033] It should be noted that the core of the embodiments of this application lies in integrating high-entropy metal sulfide particles of single-phase solid solution with carbon nanotube substrates with three-dimensional network structure to construct an ideal anode material.

[0034] In this application, the anode material is synergistically constructed from high-entropy metal sulfides and a carbon nanotube substrate with a three-dimensional conductive network. On one hand, the high-entropy metal sulfide particles, relying on the carbon nanotube substrate with a three-dimensional conductive network (carbon nanotubes possess excellent electronic conductivity and mechanical flexibility), enable the anode material to exhibit superior conductivity and sodium ion transport rate. Furthermore, its mechanical flexibility effectively mitigates the volume expansion of the high-entropy metal sulfide particles during charging and discharging, reducing the probability of electrode structure pulverization and collapse. On the other hand, the high-entropy metal sulfide particles are a single-phase solid solution formed by at least five equimolar amounts of metal elements and sulfur. This specific type of high-entropy metal sulfide can be derived from... The electrochemical performance of the material is optimized at multiple levels, including high entropy effect, lattice distortion effect, and hysteresis diffusion effect: (1) The synergistic effect of the multi-metal components regulates the bonding strength of the metal-sulfur bond, optimizes the electronic structure, and improves the intrinsic electronic conductivity of the material; (2) The high entropy structure introduces abundant defect sites and lattice distortion, providing more storage sites and diffusion channels for sodium ions, which significantly improves the sodium storage capacity; (3) The synergistic catalytic effect among the multi-metal elements reduces the reaction energy barrier of sodium ions in the insertion / extraction process and accelerates the reaction kinetics; (4) The high entropy components can effectively suppress phase transitions and element segregation during the charging and discharging process, maintain the structural stability of the material, and thus obtain excellent cycle life. Through the combined effect of these two aspects, the corresponding battery can have relatively excellent capacity, rate performance, and cycle stability.

[0035] Furthermore, it should be emphasized that the high-entropy metal sulfide particles in the single-phase solid solution constructed in this application possess a synergistic coupling of four energy storage mechanisms during charge and discharge: intercalation reaction, conversion reaction, alloying reaction, and space charge storage. Specifically, in the initial stage of discharge, sodium ions first intercalate into the interlayer or lattice gaps of the high-entropy metal sulfide, undergoing an intercalation reaction. As the discharge depth increases, the metal-sulfur bond breaks, transforming into metal nanoparticles and Na2S, achieving energy storage through the conversion reaction. Simultaneously, some metal components undergo alloying reactions with sodium, forming a sodium-metal alloy phase, contributing additional capacity. In addition, at the interface between the metal nanoparticles and Na2S, due to the spin polarization effect induced by the high-entropy component, a space charge layer is formed, storing sodium ions through interfacial capacitance. Through the synergistic effect of these four energy storage mechanisms, the corresponding battery can also possess superior capacity, rate performance, and cycle stability.

[0036] As an example, in a carbon nanotube substrate, the diameter of a single carbon nanotube is 10 nm to 50 nm (e.g., but not limited to any one of the diameters of 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm, or any range between any two), and the length is 1 μm to 20 μm (e.g., but not limited to any one of the lengths of 1 μm, 5 μm, 10 μm, 15 μm, and 20 μm, or any range between any two), and the particle size of a single high-entropy metal sulfide particle is 10 nm to 200 nm (e.g., but not limited to any one of the particle sizes of 10 nm, 50 nm, 100 nm, 150 nm, and 200 nm, or any range between any two).

[0037] In this embodiment, the diameter and length of a single carbon nanotube are simultaneously limited to the aforementioned range, so that the carbon nanotube has a more suitable size, which helps to construct a continuous three-dimensional conductive network and can provide sufficient loading sites for high-entropy metal sulfide particles. On this basis, the particle size of a single high-entropy metal sulfide particle is simultaneously limited to the aforementioned range, which enables the high-entropy metal sulfide particles to be stably loaded on the carbon nanotube and to bind the two tightly. At the same time, it also enables the high-entropy metal sulfide particles to have a larger specific surface area to provide more active sites, thereby effectively improving electron transport efficiency.

[0038] As an example, the metallic element is selected from at least five of the following: cobalt, iron, nickel, copper, zinc, manganese, chromium, manganese, molybdenum, tin, antimony, and bismuth.

[0039] In this embodiment, the types of metal elements are limited to the above-mentioned range, and the corresponding high-entropy metal sulfides can generate a better synergistic effect, thereby better optimizing the electrochemical performance of the negative electrode material. At the same time, the embodiments of this application are applicable to a wide variety of metal elements, which can provide a wide range of feasible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided by the embodiments of this application.

[0040] As an example, the metal elements are selected from cobalt, iron, manganese, chromium and nickel, and the high-entropy metal sulfide particles have a tetragonal Co3S4 phase.

[0041] As an example, the metal elements are selected from antimony, manganese, iron, cobalt, bismuth and nickel, and the high-entropy metal sulfide particles have a tetragonal Co3S4 phase (PDF#42-1448).

[0042] It should be noted that the form of the structural units in the negative electrode material that are not specifically described or limited is not limited and can be set according to the conventional choices in this field.

[0043] As an example, carbon nanotubes can be either multi-walled or single-walled, and the specific type can be adapted to meet actual needs.

[0044] Secondly, embodiments of this application provide a method for preparing a negative electrode material as provided in the first aspect embodiment, comprising the following steps: dispersing metal salts of various metal elements, carbon nanotubes, and organic ligands uniformly in a first solvent, wherein the molar amounts of various metal elements are all the same, to obtain a precursor dispersion; subjecting the precursor dispersion to a first solvothermal reaction under stirring conditions, wherein the reaction temperature is 110℃~190℃ (e.g., but not limited to any one of 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, and 190℃, or a range between any two), and the reaction time is 10 h~24 h (e.g., but not limited to times of 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, and 24 h). After the reaction, a first solid-liquid separation is performed to obtain a carbon nanotube substrate loaded with a high-entropy metal precursor. The carbon nanotube substrate loaded with the high-entropy metal precursor and the first sulfur source are dispersed in a second solvent and subjected to a second solvothermal reaction under stirring. The reaction temperature is 130℃~200℃ (e.g., but not limited to any one of 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃, or ...40℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃, or any one of 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃, or any one of 140℃, 180℃, 20h, 22h, and 24h, respectively), and the reaction time is 10 h~24 h (e.g., but not limited to 10h, 12h, 14h, 16h, 18h, 20h, 22h, and 24h, respectively). After the reaction, a second solid-liquid separation is performed to obtain a carbon nanotube substrate loaded with a high-entropy metal sulfide precursor. The carbon nanotube substrate loaded with the high-entropy metal sulfide precursor and a second sulfur source are mixed and heat-treated. The treatment temperature is 500℃~800℃ (e.g., but not limited to any one of 500℃, 600℃, 700℃ and 800℃ or any range between them), the treatment time is 1 h~5 h (e.g., but not limited to any one of 1 h, 2 h, 3 h, 4 h and 5 h or any range between them), and the heating rate is 1℃ / min~10℃ / min (e.g., but not limited to any one of 1℃ / min, 2℃ / min, 4℃ / min, 6℃ / min, 8℃ / min and 10℃ / min or any range between them), to obtain the negative electrode material.

[0045] In this application, the first solvothermal reaction is carried out under the above conditions, which enables the organic ligands and various metal ions to fully coordinate and form a high-entropy metal precursor, which grows in situ and is uniformly distributed on the surface of the carbon nanotube and the inner wall of the cavity (the carbon nanotube will simultaneously achieve self-assembly through winding and other methods during the reaction to form a carbon nanotube substrate with a three-dimensional network structure), so as to obtain a carbon nanotube substrate loaded with a high-entropy metal precursor; the second solvothermal reaction is carried out under the above conditions, which enables the metal in the high-entropy metal precursor to be fully sulfidated under the action of the first sulfur source and form a metal sulfide, so as to form a carbon nanotube substrate loaded with a high-entropy metal sulfide precursor; the heat treatment is carried out under the above reaction conditions, which enables the metal element to be further sulfidated and the metal sulfide to be fully crystallized, so as to form a single-phase solid solution of high-entropy metal sulfide particles, and also makes the formed high-entropy metal sulfide particles have the advantages of uniform particle size and suitable size, good structural stability and not easy to agglomerate. The above process can ultimately produce an anode material that is synergistically constructed from a high-entropy metal sulfide of a single-phase solid solution and a carbon nanotube substrate with a three-dimensional conductive network.

[0046] It should be noted that since the two ends of the carbon nanotube are conductive, the solvent can also enter the cavity of the carbon nanotube, so that high-entropy metal sulfide particles of single-phase solid solution can also be generated in situ inside.

[0047] It is important to emphasize that in the first solvothermal reaction stage, strict control of the reaction temperature and duration is necessary to ensure that the organic ligands and various metal ions are fully coordinated to form a high-entropy metal precursor, which is then stably and uniformly loaded onto the carbon nanotubes. This also ensures that the particle size of the high-entropy metal precursor is controlled within a suitable range.

[0048] It is important to emphasize that in the second solvothermal reaction stage, strict control of the reaction temperature and duration is necessary to ensure that the metal in the high-entropy metal precursor is fully sulfidated and forms metal sulfides under the action of the first sulfur source, so as to maintain the stoichiometric ratio of various elements and ultimately obtain high-entropy metal sulfide particles of single-phase solid solution.

[0049] It is important to emphasize that strict control of the processing temperature, duration, and heating rate is crucial during the heat treatment stage to ensure the formation of high-entropy metal sulfide particles in a single-phase solid solution. This control is essential to achieve high-entropy metal sulfide particles with uniform and suitable size, good structural stability, and resistance to agglomeration. Specifically, if the temperature is too low, the metal sulfide crystallization will be insufficient, making it difficult to form a single-phase solid solution. If the temperature is too high, the high-entropy metal sulfide particles are prone to overgrowth, resulting in significant sulfur loss and decreased structural stability. If the time is too short, sulfidation and crystallization will be incomplete; if the time is too long, the particles are prone to agglomeration and structural degradation. If the heating rate is too fast, localized overheating can occur, affecting material uniformity; if the heating rate is too slow, the process efficiency will be low, hindering practical applications.

[0050] It should be emphasized that the stepwise sulfidation process used in the embodiments of this application is also the key to preparing high-entropy metal sulfide particles of single-phase solid solution.

[0051] It should be noted that the reactions in the aforementioned stages are carried out sequentially and are closely related. Therefore, during the preparation process, it is necessary to strictly control the parameters of each stage within their respective suitable ranges.

[0052] It should be noted that the type of metal salt is not limited, and it can be at least one of nitrates, sulfates, acetates, chlorides and acetylacetone salts.

[0053] It should be noted that there is no limit to the specific amount of solvent used in each stage, and adjustments can be made according to actual needs.

[0054] As an example, in the precursor dispersion, the ratio of the total mass of the metal salts of various metal elements to the mass of carbon nanotubes is (5~15):1 (e.g., but not limited to any one of the ratios 5:1, 8:1, 10:1, 12:1, 14:1 and 15:1, or any range between the two).

[0055] In this embodiment, limiting the ratio of the total mass of metal salts of various metal elements in the precursor dispersion to the mass of carbon nanotubes within the above-mentioned range enables the high-entropy metal sulfide particles to be uniformly dispersed on the carbon nanotubes and to have a suitable loading.

[0056] As an example, in the precursor dispersion, the ratio of the total mass of the metal salts of various metal elements to the mass of the organic ligand is 1:(0.5~2), for example, but not limited to any point value or any range between the ratios of 1:0.5, 1:1, 1:1.5 and 1:2.

[0057] In this embodiment, limiting the ratio of the total mass of metal salts of various metal elements in the precursor dispersion to the mass of organic ligands within the above-mentioned range enables the organic ligands and various metal elements to coordinate more fully and thoroughly to form a high-entropy metal precursor. This ensures that the molar ratio of various metal elements in the high-entropy metal precursor remains highly consistent with the feed ratio, which in turn helps to prepare high-entropy metal sulfide particles of single-phase solid solution in the subsequent process.

[0058] As an example, the metallic element is selected from at least five of the following: cobalt, iron, nickel, copper, zinc, manganese, chromium, manganese, molybdenum, tin, antimony, and bismuth.

[0059] In this embodiment, the chemical compatibility between the aforementioned metal elements is good, which helps to efficiently form high-entropy metal sulfide particles in single-phase solid solutions.

[0060] As an example, in the first solvothermal reaction, the reaction temperature is 120°C to 180°C (e.g., but not limited to any one of 120°C, 130°C, 140°C, 150°C, 160°C, 170°C and 180°C or any range between two), and the reaction time is 12 h to 20 h (e.g., but not limited to any one of 12 h, 14 h, 16 h, 18 h and 20 h or any range between two).

[0061] In this embodiment, by further limiting the temperature and duration of the first solvothermal reaction within the aforementioned range, the organic ligands and various metal ions can be more fully and thoroughly coordinated to form a high-entropy metal precursor. At the same time, the formed high-entropy metal precursor can be more uniformly dispersed and more tightly bound on the carbon nanotubes.

[0062] As an example, the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal precursor to the mass of the first sulfur source is 1:(1.5~3), for example, but not limited to any point value or range between any two of the ratios of 1:1.5, 1:2, 1:2.5 and 1:3.

[0063] In this embodiment, limiting the ratio of the mass of the carbon nanotube substrate loaded with the high-entropy metal precursor to the mass of the first sulfur source within the above-mentioned range enables the metal in the high-entropy metal precursor to be more fully and thoroughly sulfided under the action of the first sulfur source and form a metal sulfide.

[0064] As an example, in the second solvothermal reaction, the reaction temperature is 140°C to 180°C (e.g., but not limited to any one of 140°C, 150°C, 160°C, 170°C and 180°C or any range between two), and the reaction time is 12 h to 20 h (e.g., but not limited to any one of 12 h, 14 h, 16 h, 18 h and 20 h or any range between two).

[0065] In this embodiment, by further limiting the temperature and duration of the second solvothermal reaction within the aforementioned range, the metal in the high-entropy metal precursor can be more fully and thoroughly sulfided under the action of the first sulfur source to form metal sulfides.

[0066] As an example, the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal sulfide precursor to the mass of the second sulfur source is 1:(2~5), for example, but not limited to any point value or range between any two of the ratios of 1:2, 1:3, 1:4 and 1:5.

[0067] In this embodiment, limiting the mass ratio of the carbon nanotube substrate loaded with the high-entropy metal sulfide precursor to the mass of the second sulfur source within the above-mentioned range can more effectively compensate for sulfur loss at high temperatures, so as to better maintain the stoichiometric ratio of various elements in the metal sulfide precursor, and thus further facilitate the preparation of high-entropy metal sulfide particles in a single-phase solid solution after crystallization.

[0068] As an example, in the heat treatment step, the reaction temperature is 500℃~700℃ (e.g., but not limited to any one of 500℃, 550℃, 600℃, 650℃ and 700℃ or any range between any two), the reaction time is 1 h~5 h, and the heating rate is 4℃ / min~8℃ / min (e.g., but not limited to any one of 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min and 8℃ / min or any range between any two).

[0069] In this embodiment, by further limiting the temperature, duration and heating rate of the heat treatment to the above range, the metal elements can be more fully and thoroughly sulfided and the metal sulfides can be more fully and thoroughly crystallized. Furthermore, the resulting high-entropy metal sulfide particles have the advantages of more uniform particle size, more suitable size, better structural stability and greater dispersion.

[0070] As an example, the organic ligand is selected from at least one of glyceric acid, citric acid, ethylenediaminetetraacetic acid, and tartaric acid.

[0071] In this embodiment, the selection of the above-mentioned types of organic ligands helps various metal elements to quickly coordinate and form high-entropy metal precursors and stably load them onto carbon nanotubes.

[0072] As an example, the first solvent and the second solvent are independently selected from at least one of isopropanol, ethanol, methanol and ethylene glycol.

[0073] In this embodiment, the solvent is selected from the above-mentioned types, which enables the various components to be efficiently dispersed and uniformly mixed, which helps the reaction at each stage to proceed efficiently and fully, and thus helps to finally prepare high-entropy metal sulfide particles of single-phase solid solution.

[0074] As an example, the first sulfur source and the second sulfur source are independently selected from at least one of thioacetamide, thiourea and sulfur powder.

[0075] In this embodiment, selecting the aforementioned types of sulfur source enables the metal elements to be sulfided more efficiently and thoroughly, thereby helping to ultimately prepare high-entropy metal sulfide particles of a single-phase solid solution.

[0076] It should be noted that any processes or steps not specifically described or limited during preparation can be carried out in accordance with conventional processes in this field.

[0077] As an example, a process flow diagram of the preparation method of the negative electrode material is exemplarily shown below. Figure 1 .

[0078] Thirdly, embodiments of this application provide a sodium-ion battery, wherein the negative electrode of the sodium-ion battery contains the negative electrode material provided in the first aspect embodiment.

[0079] In this application, the negative electrode of the sodium-ion battery contains the negative electrode material provided in the first aspect embodiment. Since the negative electrode material is synergistically constructed from a high-entropy metal sulfide and a carbon nanotube substrate with a three-dimensional conductive network, the negative electrode material has superior conductivity and sodium ion transport rate, and can also effectively alleviate the volume expansion of the high-entropy metal sulfide during charging and discharging, so that the sodium-ion battery has superior capacity, rate performance and cycle stability.

[0080] It should be noted that the specific form of the sodium-ion battery is not limited and can be set up in accordance with conventional forms in the field. The embodiments of this application do not impose specific limitations.

[0081] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0082] Example 1 This application provides a method for preparing a negative electrode material, including the following steps: (1) Chromium nitrate nonahydrate, manganese nitrate tetrahydrate, iron nitrate nonahydrate, cobalt nitrate hexahydrate and nickel nitrate hexahydrate were mixed in an equimolar ratio (total 25 mmol) as metal salts. The metal salts and carbon nanotubes (the diameter of a single carbon nanotube is 30 nm and the length is 1 μm) were dispersed in 50 mL of isopropanol at a mass ratio of 10:1. A uniform dispersion was formed by magnetic stirring. Then 6 mL of glyceric acid was added and the mixture was stirred and mixed to form a precursor dispersion.

[0083] (2) The precursor dispersion from step (1) was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor, sealed, and placed in an oven. The reactor was heated to 150 °C for a first solvothermal reaction for 16 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was collected by centrifugation at 10,000 rpm for 3 minutes. The product was then washed with ethanol and deionized water and dried in a vacuum oven at 80 °C for 12 hours to obtain carbon nanotube substrate powder loaded with a high-entropy metal precursor.

[0084] (3) Disperse 100 mg of the precursor powder obtained in step (2) in 50 mL of ethanol, then add 167 mg of thioacetamide and stir until homogeneous. Transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven. Heat to 160 °C for a second solvothermal reaction for 16 hours. After the reaction is complete, allow it to cool naturally to room temperature, centrifuge at 10,000 rpm for 5 minutes, collect the product, wash it with ethanol and deionized water, and dry it in a vacuum oven at 80 °C for 12 hours to obtain carbon nanotube substrate powder loaded with high-entropy metal sulfide precursor.

[0085] (4) The metal sulfide precursor obtained in step (3) is mixed with thioacetamide at a mass ratio of 1:3, placed in a tube furnace, heated to 600°C at a heating rate of 5°C / min under an argon atmosphere, held for 3 hours, and then naturally cooled to room temperature to obtain the negative electrode material.

[0086] Example 2 This application provides a method for preparing a negative electrode material, which differs from Example 1 only in that: the total molar amount of metal salt is 5 mmol, and the metal salt and carbon nanotubes (the diameter of a single carbon nanotube is 30 nm and the length is 1 μm) are dispersed in 50 mL of isopropanol at a mass ratio of 10:1. A uniform dispersion is formed by magnetic stirring, and then 1.2 mL of glyceric acid is added and the mixture is stirred and mixed to form a precursor dispersion.

[0087] Example 3 This application provides a method for preparing a negative electrode material, which differs from Example 1 only in that the metal salt composition is replaced by a mixture of antimony acetate, manganese nitrate tetrahydrate, iron nitrate nonahydrate, cobalt nitrate hexahydrate, bismuth nitrate, and nickel nitrate hexahydrate in equimolar ratio, forming a high-entropy system with different compositions.

[0088] Example 4 This application provides a method for preparing a negative electrode material, which differs from Example 1 only in that: in step (2), the temperature of the first solvothermal reaction is 120°C and the time is 24 hours; in step (3), the temperature of the second solvothermal reaction is 140°C and the time is 24 hours; in step (4), the temperature of the heat treatment is 500°C, the holding time is 5 hours, and the heating rate is maintained at 10°C / min.

[0089] Example 5 This application provides a method for preparing a negative electrode material, which differs from Example 1 only in that: in step (2), the temperature of the first solvothermal reaction is 180°C and the time is 10 hours; in step (3), the temperature of the second solvothermal reaction is 180°C and the time is 10 hours; in step (4), the temperature of the heat treatment is 700°C, the holding time is 1 hour, and the heating rate is maintained at 1°C / min.

[0090] Comparative Example 1 This application provides a comparative example of a method for preparing a negative electrode material, which differs from Example 1 only in that the molar ratio of the five metal salts is not equimolar, but is mixed in a ratio of chromium nitrate: manganese nitrate: iron nitrate: cobalt nitrate: nickel nitrate = 1:3:1:1:3.

[0091] Comparative Example 2 This application provides a comparative method for preparing a negative electrode material, which differs from Example 1 only in that: in step (1), only three metal salts, namely iron nitrate hydrate, cobalt nitrate hydrate, and nickel nitrate hydrate, are mixed in an equimolar ratio, instead of five metal elements.

[0092] Comparative Example 3 This application provides a comparative method for preparing a negative electrode material, which differs from Example 1 only in that: carbon nanotubes are not added in step (1), and metal salt and glyceric acid are mixed in isopropanol to form a precursor dispersion.

[0093] Comparative Example 4 This application provides a comparative method for preparing a negative electrode material, which differs from Example 1 only in that the temperature of the first solvothermal reaction in step (2) is 100°C.

[0094] Comparative Example 5 This application provides a comparative method for preparing a negative electrode material, which differs from Example 1 only in that the temperature of the second solvothermal reaction in step (3) is 120°C.

[0095] Comparative Example 6 This application provides a comparative example of a method for preparing a negative electrode material, which differs from Example 1 only in that the heat treatment temperature in step (4) is 450°C.

[0096] To better understand the parameter differences between the various embodiments and comparative examples, a summary explanation is provided here in tabular form, as detailed in Table 1.

[0097] Table 1

[0098] Test case (1) Morphology and crystal phase testing of negative electrode materials Test methods: The negative electrode materials obtained from Examples 1-5 and Comparative Examples 1-6 were used as samples, and the morphology and crystal phase of the samples were tested by SEM (scanning electron microscope), TEM (transmission electron microscope), and XRD (X-ray diffraction).

[0099] from Figure 2 The XRD pattern shows that the material prepared in Example 1 exhibits a broad carbon-encapsulated peak at approximately 23°, corresponding to the amorphous characteristics of carbon nanotubes. Obvious diffraction peaks appear at approximately 26.6°, 31.4°, 38.0°, 47.3°, 52.2°, and 55.0°, corresponding to the (220), (311), (400), (422), (511), and (440) crystal planes of the tetragonal Co3S4 phase (standard card: PDF#42-1228), respectively. No characteristic peaks of other impurity phases were observed, indicating that the anode material forms a high-entropy metal sulfide with a single solid solution structure and good crystallinity.

[0100] from Figure 3 The SEM images show that in the material prepared in Example 1, high-entropy metal sulfide nanoparticles are uniformly loaded in carbon nanotubes. The nanoparticles have a diameter of about 100 nm, the surface of the particles is relatively smooth, and the carbon nanotubes are intertwined to form a three-dimensional conductive network, indicating that the anode material has been successfully constructed.

[0101] from Figure 4 The TEM images further corroborate the structural features of high-entropy metal sulfide nanoparticles loaded on the surface of carbon nanotubes. The interface between the nanoparticles and carbon nanotubes is clear, with the carbon nanotubes wrapped around the nanoparticles, forming good electrical contact.

[0102] from Figure 5 The high-resolution TEM image clearly shows the lattice fringes of the high-entropy metal sulfide nanoparticles, with a crystal plane spacing of approximately 0.285 nm, corresponding to the (311) crystal plane of the tetragonal Co3S4 phase, consistent with the XRD results. The clear lattice fringes indicate that the material has high crystallinity, and no lattice fringes of other crystal phases were observed, further confirming the high purity of the single-phase solid solution structure.

[0103] See Figures 6-9 As can be seen from the SEM images, negative electrode materials constructed by high-entropy metal sulfides and carbon nanotube substrates with three-dimensional conductive networks were successfully prepared in Examples 2 to 5. Among them, the particle size of high-entropy metal sulfide nanoparticles in Examples 2 and 3 is concentrated at around 50 nm, the particle size of high-entropy metal sulfide nanoparticles in Example 4 is concentrated at around 100 nm, and the particle size of high-entropy metal sulfide nanoparticles in Example 5 is concentrated at around 200 nm.

[0104] from Figure 10 The XRD pattern shows that, in addition to the high-entropy phase diffraction peak, the material prepared in Comparative Example 1 also has several obvious impurity peaks, indicating that when the proportion of metal elements deviates from the equimolar ratio, phase separation occurs in the material, and a single-phase solid solution cannot be formed.

[0105] from Figure 11 The XRD pattern shows that, in addition to the high-entropy phase diffraction peak, the material prepared in Comparative Example 2 has obvious impurity peaks, indicating that when the types of metal elements are insufficient, phase separation also occurs in the material, and a high-entropy single-phase solid solution structure cannot be formed, which is in stark contrast to the high-entropy single-phase structure of Examples 1 to 5.

[0106] from Figure 12 The SEM images show that the material prepared in Comparative Example 3 did not form a regular nanoparticle structure. The particle morphology was irregular, the size distribution was wide, ranging from 50 nm to 500 nm, and the particles were severely aggregated. This indicates that without a carbon nanotube substrate, high-entropy metal sulfides are difficult to achieve uniform dispersion and regular morphology.

[0107] from Figure 13 The XRD pattern shows that the material prepared in Comparative Example 4 did not show the characteristic diffraction peaks of the high-entropy phase, but only broad envelope peaks were observed, indicating that when the hydrothermal temperature is below the lower limit of the protection range, the material cannot form a high-entropy single-phase solid solution structure and has poor crystallinity.

[0108] It should be noted that the XRD results of the materials prepared in Comparative Examples 5 and 6 are consistent with those of Comparative Example 4, that is, no characteristic diffraction peaks of the high-entropy phase are observed, only broad envelope peaks are observed, indicating that when the temperature of the corresponding stage is lower than the lower limit of the protection range, the material cannot form a high-entropy single-phase solid solution structure and has poor crystallinity.

[0109] (2) Electrical performance testing of negative electrode materials Test method: The negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-6 were used to prepare sodium-ion batteries, and then the performance of each battery was tested, including: first reversible capacity, first coulombic efficiency, cycle performance and rate performance. The sodium-ion battery preparation process is as follows: The prepared negative electrode material is mixed with acetylene black (conductive agent) and polyvinylidene fluoride (PVDF, binder) at a mass ratio of 8:1:1, and then added to N-methylpyrrolidone (NMP) for magnetic stirring. After 15 hours, it is evenly coated on copper foil current collector and then transferred to a vacuum drying oven. It is first dried at 55°C under normal pressure for 4 hours to remove macromolecular solvents, and then dried under vacuum at 80°C for 12 hours. After drying, it is taken out and cut into 12mm diameter discs and placed in an argon-filled glove box. The battery is then assembled in an argon-filled glove box. The electrode shell uses a 2032 coin cell, the electrode is the disc prepared above and placed in the glove box, the separator is Celgard 2320, the counter electrode and reference electrode are sodium sheets, the electrolyte is 1 M sodium trifluorosulfonate dissolved in a 1:1 volume ratio of ethylene carbonate and dimethyl carbonate, and the active material loading is 1.50 mg. cm -1 .

[0110] Electrochemical performance tests were performed on the Neware battery testing system, with a test voltage range of 0.01 to 3 V and a current density of 0.1 A / g to 20 A / g. The test results are then summarized in Tables 2 and 3.

[0111] Table 2

[0112] Table 3

[0113] As can be seen from Table 2, the negative electrode material provided in this application has excellent sodium storage performance and cycle performance. In Example 1, the anode material exhibited an initial discharge capacity of 1299.1 mAh / g, an initial charge capacity of 1002.5 mAh / g, and an initial coulombic efficiency of 77.2% at a current density of 0.1 A / g. In Example 2, the anode material had an initial discharge capacity of 1291.4 mAh / g, an initial charge capacity of 983.0 mAh / g, and an initial coulombic efficiency of 76.1%. In Example 3, the anode material had an initial discharge capacity of 1253.9 mAh / g, an initial charge capacity of 975.8 mAh / g, and an initial coulombic efficiency of 77.8%. In Example 4, the anode material had an initial discharge capacity of 1301.4 mAh / g, an initial charge capacity of 1029.1 mAh / g, and an initial coulombic efficiency of 79.1%. In Example 5, the anode material had an initial discharge capacity of 1329.6 mAh / g, an initial charge capacity of 1016.8 mAh / g, and an initial coulombic efficiency of 76.5%. The above results indicate that, thanks to the synergistic effect of multiple energy storage mechanisms such as intercalation, conversion, alloying, and space charge, the anode material provided in this application has an ultra-high sodium storage capacity and a good first coulombic efficiency. Among them, Example 4 has the highest first coulombic efficiency, and Example 5 has the highest first discharge capacity.

[0114] Regarding cycle stability, after 100 cycles at a current density of 0.1 A / g, the reversible capacities of Examples 1-5 were 968.4 mAh / g, 954.5 mAh / g, 930.0 mAh / g, 963.5 mAh / g, and 953.6 mAh / g, respectively, with capacity retention rates as high as 96.6%, 97.1%, 95.3%, 93.6%, and 93.8%, indicating that the anode material provided in this application has excellent cycle stability. Particularly at high current densities, Example 1 maintained a reversible capacity of 581.2 mAh / g after 5000 cycles at a current density of 5 A / g, and Example 4 maintained 576.3 mAh / g under the same conditions, further demonstrating its excellent cycle stability.

[0115] As can be seen from the data in Table 3, the sodium-ion batteries prepared using the negative electrode materials of Examples 1-5 exhibit excellent rate performance during high-rate charge-discharge processes. In particular, Example 1 showed reversible capacities of 1005.6, 931.4, 906.1, 856.9, 758.8, 690.5, and 566.8 mAh / g at current densities of 0.1, 0.3, 0.5, 1, 3, 5, and 10 A / g, respectively. Even when the current density returned to 0.1 A / g, its reversible capacity remained as high as 998.1 mAh / g. Example 4 showed reversible capacities of 1012.2, 919.4, 900.2, 870.1, 723.2, 679.5, and 521.0 mAh / g at current densities of 0.1, 0.3, 0.5, 1, 3, 5, and 10 A / g, respectively, reaching 1005.2 mAh / g after recovery to 0.1 A / g. Example 5 maintained a capacity of 678.1 mAh / g at a high current density of 5 A / g, reaching 996.1 mAh / g after recovery to 0.1 A / g. These results demonstrate that the anode material provided in this application maintains good structural stability and electrochemical reversibility during high-rate charge-discharge processes.

[0116] Furthermore, as can be seen from Tables 2 and 3, in Comparative Example 1, the molar ratio of the five metal salts was 1:1:1:1:3 (with a higher proportion of nickel), and the capacity obtained at each current density was lower than that in Example 1. This indicates that the high-entropy composition with non-equimolar amounts cannot form a single-phase solid solution, resulting in a decrease in electrochemical performance.

[0117] In Comparative Example 2, the ternary metal sulfide material prepared using only three metal elements (iron, cobalt, and nickel) could not form a high-entropy single-phase solid solution. The capacity obtained at each current density was lower than that of Example 1, especially at high rates where the capacity decay was more obvious, indicating that the high-entropy effect is crucial for improving rate performance.

[0118] In Comparative Example 3, no carbon nanotubes were added, and only high-entropy metal sulfide particles were prepared. The capacity obtained at each current density was lower than that of Example 1, especially at high rates. This indicates that the lack of the three-dimensional conductive network of carbon nanotubes leads to a decrease in electron transport efficiency, which cannot effectively buffer volume expansion and limits the rate performance and cycling stability.

[0119] In Comparative Examples 4 to 6, the first solvothermal reaction temperature was 100°C, the second solvothermal reaction temperature was 120°C, and the high-temperature heat treatment temperature was 450°C, all of which were lower than the lower limit of the protection scope of this application. Their electrochemical performance was significantly worse than that of Example 1, with low initial reversible capacity, poor cycle stability, and poor rate performance. This indicates that the low temperature leads to incomplete precursor formation, insufficient sulfidation and crystallization, and difficulty in forming a high-entropy single-phase solid solution structure.

[0120] In summary, this application effectively improves the electronic conductivity and ion transport rate of the anode material through a strategy of high entropy effect, three-dimensional conductive network of carbon nanotube substrate and synergistic effect of multiple energy storage mechanisms, and effectively buffers the volume expansion during charge and discharge, thereby achieving a synergistic improvement in high capacity, excellent rate performance and ultra-long cycle stability.

[0121] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A negative electrode material, characterized in that, The invention comprises a carbon nanotube substrate with a three-dimensional network structure and high-entropy metal sulfide particles, wherein the high-entropy metal sulfide particles are loaded on the surface of the carbon nanotubes in the carbon nanotube substrate and / or the inner wall of the cavity of the carbon nanotubes, and the high-entropy metal sulfide particles are made of a single-phase solid solution formed by at least five equimolar amounts of metal elements and sulfur.

2. The negative electrode material according to claim 1, characterized in that, In the carbon nanotube substrate, the diameter of a single carbon nanotube is 10 nm to 50 nm and the length is 1 μm to 20 μm, and the particle size of a single high-entropy metal sulfide particle is 10 nm to 200 nm.

3. The negative electrode material according to claim 1 or 2, characterized in that, The metallic element is selected from at least five of the following: cobalt, iron, nickel, copper, zinc, manganese, chromium, manganese, molybdenum, tin, antimony, and bismuth.

4. A method for preparing the negative electrode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Metal salts of various metal elements, carbon nanotubes, and organic ligands are all dispersed in a first solvent, wherein the molar amounts of each metal element are all the same, to obtain a precursor dispersion. The precursor dispersion was subjected to a first solvothermal reaction under stirring conditions, wherein the reaction temperature was 110℃~190℃ and the reaction time was 10 h~24 h. After the reaction was completed, a first solid-liquid separation was performed to obtain a carbon nanotube substrate loaded with a high-entropy metal precursor. The carbon nanotube substrate loaded with the high-entropy metal precursor and the first sulfur source are both dispersed in the second solvent and subjected to a second solvothermal reaction under stirring conditions. The reaction temperature is 130℃~200℃ and the reaction time is 10 h~24 h. After the reaction is completed, a second solid-liquid separation is performed to obtain the carbon nanotube substrate loaded with the high-entropy metal sulfide precursor. The carbon nanotube substrate loaded with the high-entropy metal sulfide precursor and the second sulfur source are mixed and subjected to heat treatment, wherein the treatment temperature is 500℃~800℃, the treatment time is 1 h~5 h, and the heating rate is 1℃ / min~10℃ / min, to obtain the anode material.

5. The preparation method according to claim 4, characterized in that, In the precursor dispersion, the ratio of the total mass of the metal salts of various metal elements to the mass of the carbon nanotubes is (5~15):

1. Or / and, in the precursor dispersion, the ratio of the total mass of the metal salts of various metal elements to the mass of the organic ligand is 1:(0.5~2).

6. The preparation method according to claim 4, characterized in that, In the first solvothermal reaction, the reaction temperature is 120℃~180℃ and the reaction time is 12 h~20 h.

7. The preparation method according to claim 4, characterized in that, The mass ratio of the carbon nanotube substrate loaded with the high-entropy metal precursor to the mass of the first sulfur source is 1:(1.5~3). Or / and, in the second solvothermal reaction, the reaction temperature is 140℃~180℃ and the reaction time is 12 h~20 h.

8. The preparation method according to claim 4, characterized in that, The mass ratio of the carbon nanotube substrate loaded with the high-entropy metal sulfide precursor to the mass of the second sulfur source is 1:(2~5). Or / and, in the heat treatment step, the reaction temperature is 500℃~700℃, the reaction time is 1 h~5 h, and the heating rate is 4℃ / min~8℃ / min.

9. The preparation method according to any one of claims 4 to 8, characterized in that, The organic ligand is selected from at least one of glyceric acid, citric acid, ethylenediaminetetraacetic acid, and tartaric acid; Or / and, the first solvent and the second solvent are independently selected from at least one of isopropanol, ethanol, methanol and ethylene glycol; Or / and, the first sulfur source and the second sulfur source are independently selected from at least one of thioacetamide, thiourea and sulfur powder.

10. A sodium-ion battery, characterized in that, The negative electrode of the sodium-ion battery contains the negative electrode material as described in any one of claims 1 to 3.

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