A heterogeneous hollow multi-shell structure nanocomposite and a preparation method and application thereof

Abstract

This invention belongs to the field of new energy materials, specifically relating to a heterogeneous hollow multi-shell nanocomposite material, its preparation method, and its application. The nanocomposite material is formed by nitrogen-doped carbon coating on the surface of a bimetallic sulfide, wherein the bimetallic sulfide is a composite of MoS2 and FeS. The nanocomposite material has a porous, hollow multi-shell nanosphere structure, with voids between the internal shells. This material serves as a Na... + The negative electrode material for this battery exhibits excellent electrochemical performance. Benefiting from the built-in electric field formed by the heterostructure and the unique hollow multi-shell morphology, this composite material demonstrates significant cycle stability and rate performance, and possesses rapid Na+ cycling characteristics. + Transport dynamics.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and relates to a heterogeneous hollow multi-shell structured nanocomposite material, its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Transition metal sulfides have attracted widespread attention as electrode materials for sodium-ion batteries due to their high theoretical capacity, simple preparation process, and excellent electrochemical reversibility. However, traditional single transition metal sulfides typically exhibit poor conductivity, insufficient cycle stability, and Na+ / Na ... + The slow transport kinetics and other drawbacks have greatly limited its development in practical applications. To overcome these shortcomings, researchers have significantly improved its electrochemical performance by optimizing the material's morphology and constructing composite multimetallic sulfide heterostructures. However, the inventors further discovered that the application of existing anode materials in sodium-ion batteries still faces many challenges, such as the limited structural design and the limited availability of Na+. + Issues such as slow transmission dynamics and poor cycle stability urgently require further improvement. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a heterogeneous hollow multi-shell nanocomposite material, its preparation method, and its applications. Through unique morphology design and the built-in electric field constructed at the metal sulfide heterostructure interface, this composite material exhibits excellent cycling stability and efficient Na+ extraction. + Transport dynamics, large specific surface area, and good electrolyte wettability provide a novel solution for optimizing the performance of sodium-ion battery anode materials.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, there is a heterogeneous hollow multi-shell nanocomposite material, wherein the nanocomposite material is formed by nitrogen-doped carbon coating on the surface of a bimetallic sulfide, and the bimetallic sulfide is formed by a composite of MoS2 and FeS; the nanocomposite material is a porous hollow multi-shell nanosphere structure, and there are gaps between the internal shells of the hollow multi-shell structure.

[0007] The heterogeneous hollow multi-shell nanocomposite material provided by this invention is formed by combining MoS2 and FeS, with nitrogen-doped carbon coated on the outermost layer. Its unique heterogeneous structure significantly improves the material's performance. This nanocomposite material exhibits a porous, hollow three-shell nanosphere structure, with appropriate voids remaining between each shell, which are Na+. + The transport provides an efficient channel while enhancing the structural stability and electrochemical performance of the material.

[0008] Compared to traditional single transition metal sulfide electrode materials, the MoS2 / FeS@NC composite material proposed in this invention is constructed from two transition metal sulfides, iron and molybdenum. Through the built-in electric field formed at the interface between iron sulfide and molybdenum sulfide crystals, this material significantly accelerates the Na+ oxidation process. + The transport kinetics further promote the efficient conduction of electrochemical reactions.

[0009] Furthermore, the hollow three-shell structure formed by this invention has a large specific surface area, and its abundant heterogeneous interfaces can provide a large number of reactive sites. The gaps between the shells in the multi-shell structure effectively alleviate the volume expansion problem of the electrode material during sodium storage. At the same time, by combining with carbon materials, not only can the agglomeration problem of the negative electrode material be significantly alleviated, but its conductivity can also be improved. In addition, nitrogen atoms doped into the carbon material can effectively regulate the electronic structure of the composite material, promote charge transfer, and improve specific capacity. Therefore, the nanocomposite material provided by this invention significantly improves the sodium storage capacity. + The transport dynamics of electrons and ions in the battery exhibit excellent cycle stability and rate performance, as well as rapid sodium storage performance.

[0010] On the other hand, a method for preparing the above-mentioned heterogeneous hollow multi-shell structured nanocomposite material includes the following steps:

[0011] Carbon nanospheres were obtained by dissolving sucrose in water and carrying out a hydrothermal reaction.

[0012] Carbon nanospheres were placed in a mixture containing citric acid and ferric salts (Fe3+). 3+ ) and molybdate (MoO4) 2- The carbon nanospheres were aged in the solution, and then calcined in air to obtain a hollow three-shell Fe2(MoO4)3 precursor.

[0013] Hollow three-shell MoS2 / FeS is obtained by gas-phase sulfidation treatment of the Fe2(MoO4)3 precursor and sulfur powder in an inert atmosphere. The gas-phase sulfidation process used in this invention can retain the internal morphology of the hollow three-shell of the Fe2(MoO4)3 precursor to the greatest extent, ensuring that the obtained product has a complete hollow three-shell structure.

[0014] MoS2 / FeS was mixed with dopamine and subjected to dopamine polymerization to obtain polydopamine-coated MoS2 / FeS precursor;

[0015] The polydopamine-coated MoS2 / FeS precursor is obtained by a second calcination under an inert atmosphere.

[0016] The preparation method of the present invention can prepare the above-mentioned heterogeneous hollow multi-shell nanocomposite material, and the prepared material has high structural stability, uniformity and dispersibility, thus giving it excellent sodium storage performance.

[0017] Thirdly, the application of the above-mentioned heterogeneous hollow multi-shell structured nanocomposite material in the preparation of sodium-ion batteries.

[0018] Fourthly, a sodium-ion battery negative electrode includes an active material, a conductive agent, a binder, and a current collector, wherein the active material is the aforementioned heterogeneous hollow multi-shell structured nanocomposite material.

[0019] Fifthly, a sodium-ion battery includes a positive electrode, a negative electrode, and a secondary electrolyte, wherein the negative electrode is the aforementioned negative electrode of the sodium-ion battery.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. The heterogeneous hollow multi-shell nanocomposite material provided by this invention is composed of two transition metal sulfides, iron and molybdenum. This material forms a built-in electric field through the heterogeneous structure between the two crystal interfaces, which can significantly enhance the performance of Na+. + This improves transport dynamics and effectively reduces the internal resistance of the material, thereby further optimizing its electrochemical performance.

[0022] 2. This invention uses hydrothermal reaction, aging and calcination to prepare heterogeneous transition metal sulfide / nitrogen-doped carbon nanocomposite materials with hollow multi-shell structure. The synthesis process is simple, convenient to operate, green and environmentally friendly and has low energy consumption.

[0023] 3. The heterogeneous hollow multi-shell nanocomposite material prepared by this invention has a unique three-shell structure, exhibiting excellent properties such as a large specific surface area and high porosity. This structure can effectively alleviate the volume expansion during sodium storage, significantly shorten the ion diffusion path, improve ion transport and translocation efficiency, thereby accelerating the electrochemical reaction.

[0024] 4. The heterogeneous hollow multi-shell nanocomposite material provided by the present invention alleviates the problem of anode material aggregation and improves its own conductivity by combining with carbon materials.

[0025] 5. The heterogeneous hollow multi-shell nanocomposite material provided by the present invention is coated with nitrogen-doped carbon. Due to the doping of nitrogen atoms, charge transfer is facilitated and a larger capacity is provided.

[0026] 6. The sodium-ion battery prepared using the heterogeneous hollow multi-shell nanocomposite material provided by this invention as the negative electrode material exhibits excellent cycle stability and rate performance in electrochemical tests. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0028] Figure 1 The images shown are electron microscope images of the Fe2(MoO4)3 precursor prepared in Example 1 of this invention. (a) is a scanning electron microscope (SEM) image; (b) is a transmission electron microscope (TEM) image.

[0029] Figure 2 The images shown are electron microscope images of the hollow multi-shell MoS2 / FeS@NC composite material prepared in Example 2 of the present invention. (a) is a scanning electron microscope (SEM) image; (b) is a transmission electron microscope (TEM) image.

[0030] Figure 3 The image shows the XRD pattern of the hollow multi-shell MoS2 / FeS@NC composite material prepared in Example 2 of this invention. The vertical axis represents the relative diffraction intensity, and the horizontal axis represents the 2θ diffraction angle.

[0031] Figure 4 The XPS spectrum of the hollow multi-shell MoS2 / FeS@NC composite material prepared in Example 3 of this invention is shown below.

[0032] Figure 5 The hollow multi-shell MoS2 / FeS@NC composite material prepared in Example 4 of this invention was tested at a current density of 2 A·g. –1 The following is a graph showing the cyclic performance.

[0033] Figure 6 The hollow multi-shell MoS2 / FeS@NC composite material prepared in Example 5 of this invention was tested at a current density of 0.1–10 A·g. –1 Battery charge-discharge curves for low-rate performance testing. Detailed Implementation

[0034] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0036] As introduced in the background section, existing technologies suffer from simple structural designs and Na... + To address the drawbacks of slow transport dynamics and poor cycling stability, this invention proposes a heterogeneous hollow multi-shell nanocomposite material, its preparation method, and its application.

[0037] In a typical embodiment of the present invention, a heterogeneous hollow multi-shell nanocomposite material is provided. The nanocomposite material is formed by nitrogen-doped carbon coating on the surface of a bimetallic sulfide, wherein the bimetallic sulfide is formed by a composite of MoS2 and FeS. The nanocomposite material is a porous hollow multi-shell nanosphere structure, and there are gaps between the internal shells of the hollow multi-shell structure.

[0038] The heterogeneous hollow multi-shell nanocomposite material provided by this invention possesses significant characteristics such as a large specific surface area and high porosity, providing ample channels and free space for ion transport, thereby effectively accommodating volume expansion during sodium storage. Furthermore, through compositing with carbon materials and doping with nitrogen atoms, this material significantly alleviates the aggregation problem of the anode material, while substantially improving conductivity and sodium storage performance.

[0039] In some embodiments of this implementation, the diameter of the nanosphere structure is 800–2000 nm.

[0040] Another embodiment of the present invention provides a method for preparing the above-mentioned heterogeneous hollow multi-shell nanocomposite material, comprising the following steps:

[0041] Carbon nanospheres were obtained by dissolving sucrose in water and carrying out a hydrothermal reaction.

[0042] Carbon nanospheres were aged in a solution containing citric acid, ferric salts, and molybdate. The abundant oxygen-containing groups on the surface of the carbon nanospheres captured iron ions (Fe2+) in the solution. 3+ ) and molybdate (MoO4) 2- );

[0043] A hollow three-shell Fe2(MoO4)3 precursor was obtained by first calcining aged carbon nanospheres in air.

[0044] The Fe2(MoO4)3 precursor and sulfur powder were subjected to gas-phase sulfidation treatment in an inert atmosphere to obtain hollow three-shell MoS2 / FeS.

[0045] MoS2 / FeS was mixed with dopamine and subjected to dopamine polymerization to obtain polydopamine-coated MoS2 / FeS precursor;

[0046] The polydopamine-coated MoS2 / FeS precursor is obtained by a second calcination under an inert atmosphere.

[0047] This invention synthesizes a heterogeneous hollow multi-shell nanocomposite material using a hard template method, exhibiting uniform size and good crystallinity. The crystal interfaces of the heterogeneous structure within the material form a built-in electric field, significantly enhancing the activity of metal sulfides and demonstrating excellent Na+ properties. + Transport kinetics and cycle stability. Furthermore, the material's unique hollow multi-shell structure possesses a large specific surface area and high porosity, effectively adapting to Na+ transport dynamics and cycling stability. + The volume expansion during the insertion / extraction process alleviates the aggregation problem of the negative electrode material and significantly improves its conductivity and sodium storage performance.

[0048] The ferric salts mentioned in this invention refer to compounds containing ferric ions, such as ferric chloride, ferric nitrate, and ferric acetate.

[0049] The molybdates mentioned in this invention refer to compounds containing molybdate ions, such as ammonium molybdate and sodium molybdate.

[0050] The hydrothermal reaction described in this invention refers to the reaction in which reactants are dissolved in water in a certain proportion in a closed system, and then placed in an autoclave under certain temperature and autogenous pressure of the solution, and the original mixture undergoes a reaction.

[0051] In some embodiments of this implementation, the molar ratio of ferric salt to molybdate is 1:0.45 to 0.55.

[0052] In some embodiments of this implementation, the hydrothermal reaction temperature is 160–190°C and the time is 1–1.5 h.

[0053] In some embodiments of this implementation, the solvent used in the aging solution is a mixture of water and ethanol. Specifically, the volume ratio of ethanol to water is 1:2.5 to 3.5.

[0054] In some embodiments of this implementation, the aging temperature is 40–70°C. Aging efficiency is higher under these conditions. Specifically, the aging time is 12–60 hours.

[0055] In some embodiments of this implementation, the temperature of the first calcination is 450–550°C. Specifically, the first calcination time is 2–3 hours.

[0056] In some embodiments of this implementation, the temperature of the vapor phase vulcanization treatment is 350–450°C. Specifically, the time of the vapor phase vulcanization treatment is 3–5 hours.

[0057] In some embodiments of this implementation, the addition ratio of MoS2 / FeS precursor to sulfur powder is 1:0.9 to 1.1.

[0058] In some embodiments of this implementation, the pH value of the dopamine polymerization reaction is 8.0 to 9.0.

[0059] In some embodiments of this implementation, the second calcination temperature is 350–450°C. Specifically, the second calcination time is 2–3 hours.

[0060] The preferred steps of this invention are as follows:

[0061] (1) Dissolve sucrose in water and stir until a clear and transparent solution is formed;

[0062] (2) The clear and transparent solution obtained in step (1) was subjected to a hydrothermal reaction and naturally cooled to room temperature to obtain a brownish-red precipitate;

[0063] (3) The brownish-red precipitate obtained in step (2) was centrifuged, washed, dried and ground with deionized water and anhydrous ethanol to collect carbon nanospheres;

[0064] (4) The carbon nanospheres obtained in step (3) are dispersed in an aqueous solution of anhydrous citric acid, ammonium heptamolybdate tetrahydrate and ferric chloride hexahydrate. After aging under reflux conditions, a black precipitate is obtained.

[0065] (5) The black precipitate obtained in step (4) was centrifuged, washed and dried with anhydrous ethanol, ground and collected, and then calcined in air to obtain Fe2(MoO4)3 with a hollow three-shell structure.

[0066] (6) The hollow three-shell structure Fe2(MoO4)3 obtained in step (5) and sulfur powder are placed downstream and upstream of the gas flow direction, respectively, and gas phase sulfidation is carried out under argon atmosphere to obtain the hollow three-shell structure MoS2 / FeS precursor.

[0067] (7) The hollow three-shell structured MoS2 / FeS precursor obtained in step (6) was dispersed in Tris buffer solution, and then dopamine hydrochloride was added to it and stirred. The mixture was then washed and dried by centrifugation with deionized water to obtain the MoS2 / FeS@PDA complex.

[0068] (8) The MoS2 / FeS@PDA composite obtained in step (7) is calcined under an argon atmosphere to obtain MoS2 / FeS@NC, which is a hollow three-shell heterostructure transition metal sulfide / nitrogen-doped carbon nanocomposite material.

[0069] Specifically, in step (1), the stirring time is 30 to 50 minutes, preferably 45 minutes.

[0070] In step (2), the reaction conditions for the hydrothermal process are: reaction at 160-190℃ for 1-1.5h, and the hydrothermal conditions are further preferred to be reaction at 170℃ for 1h.

[0071] In step (3), the centrifugation conditions are to use deionized water and anhydrous ethanol, and to centrifuge and wash 3 to 6 times. The preferred centrifugation conditions are to use deionized water for 3 centrifugations and anhydrous ethanol for 2 centrifugations.

[0072] In step (4), the reflux condensation conditions are 40-70°C, the continuous heat preservation and stirring time is 12-60h, and the optimal stirring time is 48h.

[0073] In step (5), the calcination conditions are calcination at 450-550℃ for 2-3 hours, and the preferred calcination temperature is 500℃ for 2 hours.

[0074] In step (6), the calcination conditions are calcination at 350-550℃ for 3-5 hours, and the preferred calcination temperature is 400℃ for 3 hours.

[0075] In step (7), the stirring time is 12-48 hours, with 48 hours being the preferred optimal stirring time. The mixture is centrifuged and washed 3-6 times, preferably 4 times with deionized water.

[0076] In step (8), the calcination temperature is 350-550℃, and the optimal temperature is further preferred to be 400℃.

[0077] A third embodiment of the present invention provides an application of the above-mentioned heterogeneous hollow multi-shell structured nanocomposite material in the preparation of sodium-ion batteries.

[0078] A fourth embodiment of the present invention provides a sodium-ion battery negative electrode, comprising an active material, a conductive agent, a binder, and a current collector, wherein the active material is the aforementioned heterogeneous hollow multi-shell structured nanocomposite material.

[0079] In some embodiments of this implementation, the mass ratio of the active material, conductive agent, and binder is 65-80:15-30:10-15.

[0080] In some embodiments of this implementation, the conductive agent is acetylene black, Ketjen black, or carbon nanotubes, etc. Ketjen black has higher conductivity, and using Ketjen black as the conductive agent can reduce the amount of conductive agent used.

[0081] In some embodiments of this implementation, the binder is polyvinylidene fluoride, sodium carboxymethyl cellulose, or polyacrylic acid, etc. When polyvinylidene fluoride is used as the binder, an organic solvent is required to disperse the materials. When sodium carboxymethyl cellulose or polyacrylic acid is used as the binder, water is required to disperse the materials. The present invention preferably uses sodium carboxymethyl cellulose as the binder.

[0082] A fifth embodiment of the present invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, and a secondary electrolyte, wherein the negative electrode is the aforementioned negative electrode of the sodium-ion battery.

[0083] In some embodiments of this implementation, the positive electrode is a sodium sheet.

[0084] In some embodiments of this implementation, the secondary electrolyte used is of type NP-005 or NC-034. NP-005 uses sodium hexafluorophosphate as the electrolyte and diethylene glycol dimethyl ether as the solvent; NC-034 uses sodium perchlorate as the electrolyte and a mixed solution of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio 1:1:1) as the solvent.

[0085] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0086] Example 1

[0087] A method for preparing a hollow multi-shell Fe2(MoO4)3 precursor includes the following steps:

[0088] Under magnetic stirring, 4 g of sucrose was dissolved in 20 ml of water, and the sucrose solution was transferred to a reaction vessel with a polytetrafluoroethylene liner (capacity 100 mL) and heated at 170 °C for 1 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and then dried in a forced-air drying oven at 60 °C for 6 h to obtain brownish-red carbon nanospheres. 2.85 g of anhydrous citric acid, 13.3 g of ferric chloride hexahydrate, and 4.414 g of ammonium heptamolybdate tetrahydrate (molar ratio Fe:Mo = 1:0.5) were dissolved in 10 mL of anhydrous ethanol and 30 mL of deionized water. 10 mg of carbon nanospheres were dispersed in the mixed solution and sonicated for 60 min. The dispersion was then heated to 40 °C under reflux and aged for 48 h. After naturally cooling to room temperature, the precipitate was collected by centrifugation, washed several times with anhydrous ethanol, and then dried at 60°C for 6 hours in a forced-air drying oven. The aged carbon nanospheres were then placed in a tube furnace and calcined at 500°C in an air atmosphere for 2 hours to obtain a hollow multi-shell structure Fe2(MoO4)3 precursor.

[0089] The scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the hollow multi-shell Fe2(MoO4)3 precursor spheres obtained in this embodiment are shown below. Figure 1 (a) and Figure 1 (b), Figure 1 This indicates that the Fe2(MoO4)3 precursor spheres prepared in this embodiment have a hollow three-shell structure.

[0090] Example 2

[0091] The Fe2(MoO4)3 precursor powder prepared in Example 1 and sulfur powder were placed downstream and upstream of the gas flow direction in a tube furnace, respectively, and calcined at 400°C for 3 h in Ar atmosphere to obtain black MoS2 / FeS. 80 mg of MoS2 / FeS powder was dispersed in 100 mL of Tris buffer solution (pH = 8.5) and sonicated for 1 h to ensure uniform dispersion. Subsequently, 30 mg of dopamine hydrochloride was added to the dispersion and stirred continuously for 8 h. The precipitate was collected by centrifugation, washed several times with deionized water, and then dried in a 60°C forced-air drying oven for 10 h. The collected MoS2 / FeS@PDA was placed in a tube furnace and calcined at 400°C for 2 h in an argon atmosphere to obtain a hollow three-shell structured MoS2 / FeS@NC.

[0092] Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the hollow three-shell heterostructured transition metal sulfide / nitrogen-doped carbon nanocomposite material prepared in this embodiment are shown below. Figure 2 (a) and Figure 2 (b), Figure 2(a) This indicates that the prepared MoS2 / FeS@NC has a nanosphere structure with a diameter of 800–2000 nm. Figure 2 (b) indicates that the prepared MoS2 / FeS@NC has a hollow three-shell structure. This is shown in the X-ray powder diffraction pattern. Figure 3 This demonstrates the successful preparation of the MoS2 / FeS@NC heterostructure.

[0093] Example 3

[0094] The Fe2(MoO4)3 precursor powder and sulfur powder prepared in Example 1 were placed downstream and upstream of the gas flow direction in a tube furnace, respectively, and calcined at 400°C for 3 h in Ar atmosphere to obtain black MoS2 / FeS. 80 mg of MoS2 / FeS powder was dispersed in 100 mL of Tris buffer solution (pH = 8.5) and sonicated for 1 h to ensure uniform dispersion. Subsequently, 30 mg of dopamine hydrochloride was added to the dispersion and stirred continuously for 8 h. The precipitate was collected by centrifugation, washed several times with deionized water, and then dried in a 60°C forced-air drying oven for 10 h. The collected MoS2 / FeS@PDA was placed in a tube furnace and calcined at 350°C for 2 h in an argon atmosphere to obtain a hollow three-shell structured MoS2 / FeS@NC.

[0095] The hollow three-shell structure MoS2 / FeS@NC obtained in this embodiment was used as the negative electrode material for a sodium-ion battery. The negative electrode material was mixed with Ketjen Black and sodium carboxymethyl cellulose at a mass ratio of 8:1:1 in deionized water until homogeneous. This mixture was then coated onto copper foil and vacuum dried to obtain the negative electrode. The positive electrode used was a sodium sheet. The secondary electrolyte was NP-005, with sodium hexafluorophosphate as the electrolyte and diethylene glycol dimethyl ether as the solvent. A sodium-ion battery was then assembled. The XPS spectra were analyzed. Figure 4 This confirms the existence of five elements: Mo, Fe, S, N, and C.

[0096] Example 4

[0097] The Fe2(MoO4)3 precursor powder and sulfur powder prepared in Example 1 were placed downstream and upstream of the gas flow direction in a tube furnace, respectively, and calcined at 400°C for 3 h in Ar atmosphere to obtain black MoS2 / FeS. 80 mg of MoS2 / FeS powder was dispersed in 100 mL of Tris buffer solution (pH = 8.5) and sonicated for 1 h to ensure uniform dispersion. Subsequently, 30 mg of dopamine hydrochloride was added to the dispersion and stirred continuously for 8 h. The precipitate was collected by centrifugation, washed several times with deionized water, and then dried in a 60°C forced-air drying oven for 10 h. The collected MoS2 / FeS@PDA was placed in a tube furnace and calcined at 350°C for 2 h in an argon atmosphere to obtain a hollow three-shell structured MoS2 / FeS@NC.

[0098] The hollow three-shell structure MoS2 / FeS@NC obtained in this embodiment was used as the negative electrode material for a sodium-ion battery. The negative electrode material was mixed with Ketjen Black and sodium carboxymethyl cellulose at a mass ratio of 7:2:1 in deionized water until homogeneous. This mixture was then coated onto copper foil and vacuum dried to obtain the negative electrode. The positive electrode was a sodium sheet, and the secondary electrolyte used was NP-005, in which sodium hexafluorophosphate was the electrolyte and diethylene glycol dimethyl ether was the solvent. A sodium-ion battery was then assembled. (2Ag) –1 The discharge specific capacity after 3000 charge-discharge cycles at the specified current density is 349.3 mA hg. –1 See Figure 5 .

[0099] Example 5

[0100] The Fe2(MoO4)3 precursor powder and sulfur powder prepared in Example 1 were placed downstream and upstream of the gas flow direction in a tube furnace, respectively, and calcined at 400°C for 3 h in Ar atmosphere to obtain black MoS2 / FeS. 80 mg of MoS2 / FeS powder was dispersed in 100 mL of Tris buffer solution (pH = 8.5) and sonicated for 1 h to ensure uniform dispersion. Subsequently, 30 mg of dopamine hydrochloride was added to the dispersion and stirred continuously for 8 h. The precipitate was collected by centrifugation, washed several times with deionized water, and then dried in a 60°C forced-air drying oven for 10 h. The collected MoS2 / FeS@PDA was placed in a tube furnace and calcined at 350°C for 2 h in an argon atmosphere to obtain a hollow three-shell structured MoS2 / FeS@NC.

[0101] The hollow three-shell structure MoS2 / FeS@NC obtained in this embodiment was used as the negative electrode material for a sodium-ion battery. The negative electrode material was mixed with Ketjen Black and sodium carboxymethyl cellulose at a mass ratio of 7:2:1 in deionized water until homogeneous. The mixture was then coated onto copper foil and vacuum dried to obtain the negative electrode. The positive electrode was a sodium sheet, and the secondary electrolyte used was NP-005, in which sodium hexafluorophosphate was used as the electrolyte and diethylene glycol dimethyl ether was used as the solvent. A sodium-ion battery was then assembled. Its performance at current densities of 0.1–10 Ag was tested. –1 At a current density of [value], its charge-discharge curve is shown below. Figure 6 At 0.1, 0.2, 0.5, 1, 2, 5 and 10 Ag –1 At current densities of 688.5, 558.73, 486.02, 460.48, 427.17, 400.21, and 372.67 mA hg, respectively, were obtained. -1 The specific discharge capacity.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nanocomposite of a heterogeneous hollow multi-shell structure, characterized in that, The nanocomposite material is formed by nitrogen-doped carbon coating on the surface of a bimetallic sulfide, which is formed by a composite of MoS2 and FeS. The nanocomposite material is a porous hollow multi-shell nanosphere structure, with gaps between the internal shells of the hollow multi-shell structure. The method for preparing the heterogeneous hollow multi-shell nanocomposite material is characterized by comprising the following steps: Carbon nanospheres were obtained by dissolving sucrose in water and carrying out a hydrothermal reaction. Carbon nanospheres were aged in a mixed solution of ferric salt, molybdenum salt and citric acid. The aged carbon nanospheres were then subjected to a first calcination in air to obtain a hollow three-shell Fe2(MoO4)3 precursor. The Fe2(MoO4)3 precursor and sulfur powder were subjected to gas-phase sulfidation treatment in an inert atmosphere to obtain hollow three-shell MoS2 / FeS. MoS2 / FeS was mixed with dopamine and subjected to dopamine polymerization to obtain polydopamine-coated MoS2 / FeS precursor; The polydopamine-coated MoS2 / FeS precursor is obtained by a second calcination under an inert atmosphere.

2. The nanocomposite of heterogeneous hollow multi-shell structure according to claim 1, characterized in that, The diameter of the nanosphere structure is 800~2000 nm.

3. A method for preparing the nanocomposite of the heterogeneous hollow multi-shell structure according to claim 1, characterized by, Includes the following steps: Carbon nanospheres were obtained by dissolving sucrose in water and carrying out a hydrothermal reaction. Carbon nanospheres were aged in a mixed solution of ferric salt, molybdenum salt and citric acid. The aged carbon nanospheres were then subjected to a first calcination in air to obtain a hollow three-shell Fe2(MoO4)3 precursor. The Fe2(MoO4)3 precursor and sulfur powder were subjected to gas-phase sulfidation treatment in an inert atmosphere to obtain hollow three-shell MoS2 / FeS. MoS2 / FeS was mixed with dopamine and subjected to dopamine polymerization to obtain polydopamine-coated MoS2 / FeS precursor; The polydopamine-coated MoS2 / FeS precursor is obtained by a second calcination under an inert atmosphere.

4. The method for preparing the heterogeneous hollow multi-shell nanocomposite material as described in claim 3, characterized in that, The molar ratio of ferric salt to molybdate is 1:0.45~0.55; Alternatively, the hydrothermal reaction temperature is 160~190 °C, and the time is 1~1.5 h; Alternatively, the aging temperature is 40~70 °C.

5. The method for preparing the heterogeneous hollow multi-shell nanocomposite material as described in claim 3, characterized in that, In the solution used for aging, the solvent is a mixture of water and ethanol, preferably, the volume ratio of ethanol to water is 1:2.5~3.5; Alternatively, the temperature of the first calcination is 450~550 °C; Alternatively, the pH for dopamine polymerization is 8.0~9.0; Alternatively, the temperature of the second calcination is 350~450 °C.

6. The application of a heterogeneous hollow multi-shell nanocomposite material according to claim 1 or 2, or a heterogeneous hollow multi-shell nanocomposite material obtained by any of the preparation methods according to claims 3 to 5, in the preparation of sodium-ion batteries.

7. A sodium-ion battery anode comprising an active material, a conductive agent, a binder, and a current collector, characterized in that, The active material is the heterogeneous hollow multi-shell nanocomposite material according to claim 1 or 2, or the heterogeneous hollow multi-shell nanocomposite material obtained by any of the preparation methods according to claims 3 to 5.

8. The sodium-ion battery anode of claim 7, wherein the carbon-based material is selected from the group consisting of graphite, hard carbon, soft carbon, and combinations thereof. The mass ratio of active material, conductive agent and binder is 65~80:15~30:10~15; Alternatively, the conductive agent may be acetylene black, Ketjen black, or carbon nanotubes; Or, the binder is polyvinylidene fluoride, sodium carboxymethyl cellulose or polyacrylic acid.

9. A sodium-ion battery comprising a positive electrode, a negative electrode and a secondary electrolyte, characterized in that, The negative electrode is the above-mentioned sodium-ion battery negative electrode.

10. The sodium-ion battery of claim 9, wherein the sodium-ion battery is characterized by, The positive electrode is sodium sheet.

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