A yolk-shell structure cobalt vanadium sulfide@hollow carbon nanospheres and a preparation method thereof

Abstract

The application relates to the technical field of new energy materials, and discloses a yolk-shell structure cobalt-vanadium sulfide@ hollow carbon nanospheres and a preparation method thereof. 1.097 The CoS 1.097 / V7S8 composite sulfide is a yolk, the hollow carbon sphere is a shell, and a reserved buffer gap is constructed between the yolk and the shell. The target material is prepared through a template mediation process, a carbon layer coating process, a cobalt-vanadium sulfide precursor loading process, a hydrothermal sulfidation process, an etching process and a post-processing process. The yolk-shell structure cobalt-vanadium sulfide@ hollow carbon nanosphere material prepared by the application has high capacity, long cycle stability and high rate performance, solves the pain point of insufficient cycle life of existing cobalt-vanadium sulfides, and can promote the large-scale application of sodium ion batteries in the large-scale energy storage field.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and more specifically, to a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure and its preparation method. Background Technology

[0002] With the global concept of carbon neutrality gaining traction and the energy revolution accelerating, the large-scale development and utilization of renewable energy sources (solar, wind, etc.) has created an urgent need for efficient energy storage technologies. Although lithium-ion batteries are widely used in electric vehicles and small-scale energy storage, the limited and uneven distribution of lithium resources has led to a continuous increase in raw material costs. Furthermore, lithium batteries suffer from drawbacks such as the risk of over-discharge and high costs of current collectors (copper foil), making it difficult to meet the low-cost, large-scale application requirements of large-scale energy storage systems.

[0003] Currently, among transition metal sulfides, cobalt-based sulfides (Co9S8, CoS, CoS2, etc.) have become important research targets for sodium-ion battery anode materials due to their considerable theoretical capacity, low cost, and good redox activity. However, they have three major problems when used alone: ​​① severe volume expansion, with an expansion rate of 120%~180% during charge and discharge, leading to pulverization of active materials and collapse of electrode structure; ② poor inherent conductivity, slow interfacial reaction kinetics, and poor rate performance; ③ easy formation of soluble polysulfides during charge and discharge, resulting in irreversible capacity decay and reduced coulombic efficiency. Vanadium-based sulfides (such as V7S8, VS2) have relatively excellent electronic conductivity and structural stability, but their theoretical capacity is lower than that of cobalt-based sulfides, making it difficult to meet the high energy density requirements when used alone. To leverage synergistic effects, existing technology CN114853085B developed a cobalt-vanadium composite sulfide. This design utilizes cobalt-based sulfides to provide high capacity and vanadium-based sulfides to enhance conductivity, achieving complementary performance. Its initial discharge capacity reaches 833.86 mAh·g. -1 However, these composite sulfides are still single nanostructures (such as stacked nanoflowers) and lack a buffer space designed to address volume expansion issues, resulting in unsatisfactory cycling stability and difficulty in meeting the long cycle life requirements of practical applications.

[0004] While modification methods such as carbon coating and three-dimensional aerogels can address some of the issues, the weak interfacial bonding between the carbon layer and the active material, the high risk of porous structure collapse, and the need to improve cycle stability remain problems. Furthermore, traditional modification methods (such as nanostructuring and heterostructure construction) have not fundamentally solved the spatial buffering problem of volume expansion. To date, however, no literature or patent reports have described a technical solution that uses a "yolk-shell" structure design to reserve a hollow region of a specific width between the cobalt vanadium sulfide and the carbon shell, simultaneously addressing the three core issues of volume expansion, poor conductivity, and polysulfide shuttle.

[0005] Therefore, developing a new material that simultaneously addresses the issues of volume expansion buffering and conductivity enhancement is of significant practical importance. Summary of the Invention

[0006] In view of this, the present invention proposes a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure and its preparation method, aiming to solve the contradictions in the current technology of material pulverization, electrode structure damage, insufficient material conductivity and poor cycle stability caused by polysulfide shuttle effect due to the drastic volume expansion during the charge and discharge process of cobalt vanadium sulfide, and the inability of existing structures to achieve both high capacity and long cycle life.

[0007] This invention proposes a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure, wherein the egg yolk is cobalt vanadium sulfide, the shell of the egg yolk-shell structure is a hollow carbon nanosphere, and a reserved gap is formed between the egg yolk and the shell.

[0008] Furthermore, the composition of the cobalt vanadium sulfide is CoS 1.097 A mixture of Co and V7S8, with a particle size of 50-100 nm. 2 + With V 3+ The molar ratio is (1~5):1.

[0009] Furthermore, the thickness of the hollow carbon nanospheres is 10~30nm; the width of the reserved gaps is 30~80nm.

[0010] Furthermore, a method for preparing egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres includes the following steps: (1) Preparation of SiO2 nanosphere template: Tetraethyl orthosilicate, ammonia, ethanol and deionized water were mixed, stirred evenly and washed by centrifugation and dried to obtain SiO2 nanospheres; (2) Carbon coating: SiO2 nanospheres were dispersed in an aqueous solution of carbon source, urea was added, and then a hydrothermal reaction was carried out. After cooling, the nanospheres were centrifuged and washed, and then carbonized under an Ar atmosphere to obtain SiO2@C core-shell nanospheres. (3) Cobalt vanadium sulfide precursor loading: SiO2@C core-shell nanospheres were dispersed in deionized water, CoCl2·6H2O and VCl3 were added, and after stirring evenly, urea and thioacetamide were added and stirring was continued to obtain a mixed solution; (4) Hydrothermal sulfidation and template etching: The mixture from step (3) is subjected to hydrothermal sulfidation reaction, cooled and centrifuged to collect the precipitate, and soaked in etching agent to obtain etched precipitate; (5) Post-treatment: The etched precipitate was washed with deionized water and ethanol alternately 3 to 5 times, vacuum dried, and ground to obtain egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres.

[0011] Furthermore, the stirring parameters in step (1) are: temperature 25~40℃, time 2~6h; the drying temperature is 60~80℃; and the particle size of the SiO2 nanospheres is 100~200nm.

[0012] Furthermore, in step (2), the carbon source aqueous solution is glucose or sucrose, and the mass concentration of the carbon source aqueous solution is 5%~15%; the mass ratio of the carbon source to urea is 1:2~5; the mass ratio of the carbon source to SiO2 nanospheres is 1:1~3; the hydrothermal reaction parameters are: temperature 160~180℃, time 8~12h; and the carbonization parameters are: temperature 600~800℃, time 2~4h.

[0013] Furthermore, the total molar amount of CoCl2·6H2O and VCl3 mentioned in step (3) is 1 mmol, and Co 2+ and V 3+ The molar ratio of urea to Co is 1~5:1; 2+ The molar ratio of the thioacetamide to Co is 10~50:1; 2+ The molar ratio is 1~10:1; the stirring parameters are: rotation speed 300~500 r / min, time 0.5~2 h.

[0014] Furthermore, the hydrothermal sulfidation reaction parameters in step (4) are: temperature 80~160℃, time 8~24h; the etching agent is 0.5~2mol / L hydrofluoric acid solution or sodium hydroxide solution; the soaking is soaking for 6~12h.

[0015] Furthermore, the vacuum drying parameters in step (5) are: vacuum degree -0.08~-0.1MPa, temperature 60~80℃, and time 12~24h.

[0016] This invention also provides the application of the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres described in the above technical solution, specifically the application of the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres in the preparation of sodium-ion battery anode materials.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The spatial buffer mechanism with reserved gaps in this invention can accommodate volume expansion and prevent material pulverization; the physical barrier mechanism of the hollow carbon shell can suppress polysulfide diffusion and improve coulombic efficiency; the conductivity enhancement mechanism of the carbon shell can also reduce electron transport resistance and optimize rate performance; it breaks through the contradiction between high capacity and long cycle time in existing technologies and achieves synergistic improvement in capacity, cycle stability and rate performance.

[0018] The cobalt vanadium sulfide (yolk)-hollow carbon nanospheres (shell)-reserved void core-shell structure of the present invention actively constructs reserved voids through the three-in-one design of active center, structural support and spatial buffer, fundamentally solving the volume expansion problem from the structure. At the same time, the carbon shell provides additional conductive path and mechanical support.

[0019] In this invention, the reserved gap between the yolk and the shell can fully accommodate the volume expansion of cobalt vanadium sulfide during charging and discharging, thus avoiding material pulverization and electrode structure damage.

[0020] In this invention, the mechanical support of the carbon shell inhibits material agglomeration, while the highly conductive carbon shell accelerates electron transport and reduces polarization loss.

[0021] In this invention, the carbon shell physically blocks the diffusion of polysulfides, improving the battery coulombic efficiency, maintaining the high specific capacity of cobalt vanadium sulfides, and significantly improving cycle life.

[0022] The preparation method described in this invention is an improvement on the traditional hydrothermal method. The added steps are simple and low-cost, making it suitable for large-scale industrial production. Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0024] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] This invention provides a cobalt vanadium sulfide@hollow carbon nanosphere structure with an egg yolk-shell structure. The egg yolk is cobalt vanadium sulfide, and the shell in the egg yolk-shell structure is a hollow carbon nanosphere, with a reserved gap between the egg yolk and the shell.

[0029] In this invention, the cobalt vanadium sulfide has the composition CoS 1.097 The mixture of Co and V7S8 has a preferred particle size of 50-100 nm, more preferably 60-100 nm. 2+ With V 3+ The preferred molar ratio is 1 to 5:1, and more preferably 2 to 5:1.

[0030] In this invention, the egg yolk is selected as the cobalt vanadium sulfide in the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres, wherein the cobalt vanadium sulfide comprises CoS 1.097 It is a defective cobalt sulfide crystal phase with a Co to S atomic ratio of 1:1.097, which can provide high-capacity active sites and improve the theoretical specific capacity of the material; V7S8 is a definite crystal phase structure with a vanadium to sulfur atomic ratio of 7:8. It is a highly conductive transition metal sulfide with a stable structure and excellent rate capability and cycling characteristics. Its function is to enhance the overall electronic conductivity of the material, buffer the volume expansion during charge and discharge, and improve the cycling stability.

[0031] In this invention, the thickness of the hollow carbon nanospheres is preferably 10-30 nm, more preferably 15-30 nm; the width of the reserved gaps is preferably 30-80 nm, more preferably 40-80 nm.

[0032] In this invention, the shell is selected as hollow carbon nanospheres, which provide a conductive path, mechanical support and physical barrier of polysulfides; the reserved gaps are used to accommodate the volume expansion during the charging and discharging process, and avoid material pulverization and electrode collapse.

[0033] In this invention, a method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure includes the following steps: (1) Preparation of SiO2 nanosphere template: Tetraethyl orthosilicate, ammonia, ethanol and deionized water were mixed, stirred evenly and washed by centrifugation and dried to obtain SiO2 nanospheres; (2) Carbon coating: SiO2 nanospheres were dispersed in an aqueous solution of carbon source, urea was added, and then a hydrothermal reaction was carried out. After cooling, the nanospheres were centrifuged and washed, and then carbonized under an Ar atmosphere to obtain SiO2@C core-shell nanospheres. (3) Cobalt vanadium sulfide precursor loading: SiO2@C core-shell nanospheres were dispersed in deionized water, CoCl2·6H2O and VCl3 were added, and after stirring evenly, urea and thioacetamide were added and stirring was continued to obtain a mixed solution; (4) Hydrothermal sulfidation and template etching: The mixture from step (3) is subjected to hydrothermal sulfidation reaction, cooled and centrifuged to collect the precipitate, and soaked in etching agent to obtain etched precipitate; (5) Post-treatment: The etched precipitate was washed with deionized water and ethanol alternately 3 to 5 times, vacuum dried, and ground to obtain egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres.

[0034] In this invention, the SiO2 nanosphere template provides a size reference for the core-shell structure; the carbon layer coating includes hydrothermal carbon source deposition and high-temperature carbonization, which can construct a hollow carbon shell to achieve structural support and enhanced conductivity; the template etching can remove the SiO2 template and form reserved voids.

[0035] In this invention, the stirring parameters in step (1) are preferably: temperature 25~40℃, time 2~6h, more preferably temperature 30~40℃, time 3~6h; the drying temperature is preferably 60~80℃, more preferably 65~80℃; the particle size of the SiO2 nanospheres is preferably 100~200nm, more preferably 120~200nm.

[0036] In this invention, the carbon source aqueous solution in step (2) is glucose or sucrose, and the mass concentration of the carbon source aqueous solution is preferably 5%~15%, more preferably 8%~15%; the mass ratio of the carbon source to urea is preferably 1:2~5, more preferably 1:3~5; the mass ratio of the carbon source to SiO2 nanospheres is preferably 1:1~3, more preferably 1:2~3; the hydrothermal reaction parameters are preferably: temperature 160~180℃, time 8~12h, more preferably temperature 165~180℃, time 9~12h; the carbonization parameters are preferably: temperature 600~800℃, time 2~4h, more preferably temperature 650~800℃, time 2.5~4h.

[0037] In this invention, the total molar amount of CoCl2·6H2O and VCl3 in step (3) is preferably 1 mmol, and Co2+ and V 3+ The preferred molar ratio of urea to Co is 1~5:1, more preferably 2~5:1; 2+ The preferred molar ratio is 10~50:1, more preferably 20~50:1; the thioacetamide and Co 2+ The preferred molar ratio is 1~10:1, more preferably 2~10:1; the preferred stirring parameters are: rotation speed 300~500 r / min, time 0.5~2 h, more preferably rotation speed 350~500 r / min, time 1~2 h.

[0038] In this invention, the hydrothermal sulfidation reaction parameters in step (4) are preferably: temperature 80~160℃, time 8~24h, more preferably temperature 90~160℃, time 9~24h; the etching agent is preferably a 0.5~2mol / L hydrofluoric acid solution or sodium hydroxide solution, more preferably a 0.7~2mol / L hydrofluoric acid solution or sodium hydroxide solution; the soaking is preferably soaking for 6~12h, more preferably soaking for 8~12h.

[0039] The hydrothermal sulfidation reaction described in this invention promotes the sulfidation reaction and crystal growth of cobalt vanadium ions with thioacetamide (TAA) under high pressure, thereby achieving the sulfidation and crystallization of the cobalt vanadium precursor (forming CoS). 1.097 / V7S8 dual-phase structure).

[0040] In this invention, the vacuum drying parameters in step (5) are preferably: vacuum degree -0.08~-0.1MPa, temperature 60~80℃, and time 12~24h, and more preferably vacuum degree -0.09~-0.1MPa, temperature 65~80℃, and time 15~24h.

[0041] This invention also provides the application of the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres described in the above technical solution, specifically the application of the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres in the preparation of sodium-ion battery anode materials.

[0042] In this invention, unless otherwise specified, all raw materials required for preparation are commercially available products well known to those skilled in the art.

[0043] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1 (1) Preparation of SiO2 nanosphere template: Tetraethyl orthosilicate, ammonia, ethanol and deionized water were mixed, stirred at 30°C for 6 h and centrifuged and washed, and then dried at 65°C to obtain SiO2 nanospheres; (2) Carbon coating: SiO2 nanospheres were dispersed in an 8% glucose aqueous solution with a mass ratio of 1:2 to the glucose aqueous solution and SiO2 nanospheres. Urea was added, and then a hydrothermal reaction was carried out at 165°C for 12 h. After cooling, the nanospheres were centrifuged and washed, and then carbonized at 650°C in an Ar atmosphere for 4 h to obtain SiO2@C core-shell nanospheres with a particle size of 120 nm. (3) Cobalt vanadium sulfide precursor loading: SiO2@C core-shell nanospheres were dispersed in deionized water, and CoCl2·6H2O and VCl3 were added, wherein the concentration of CoCl2·6H2O and VCl3 was 2:1. After stirring at 350 r / min for 2 h to homogenize, urea and thioacetamide were added and stirring was continued to obtain a mixed solution. (4) Hydrothermal sulfidation and template etching: The mixture in step (3) was subjected to hydrothermal sulfidation reaction at 90°C for 24 hours. After cooling, the precipitate was collected by centrifugation and soaked in 0.7 mol / L hydrofluoric acid solution for 12 hours to obtain the etched precipitate. (5) Post-treatment: The etched precipitate was washed three times with deionized water and ethanol alternately, and then vacuum dried for 24 h under vacuum conditions of -0.09 MPa and 65 °C. After grinding, cobalt vanadium sulfide with egg yolk-shell structure was obtained @ hollow carbon nanospheres.

[0045] Example 2 (1) Preparation of SiO2 nanosphere template: Tetraethyl orthosilicate, ammonia, ethanol and deionized water were mixed, stirred at 35°C for 4 h and centrifuged and washed, and then dried at 70°C to obtain SiO2 nanospheres with a particle size of 150 nm. (2) Carbon coating: SiO2 nanospheres were dispersed in a 10% sucrose aqueous solution with a mass ratio of 1:2 to the sucrose aqueous solution and SiO2 nanospheres. Urea was added, and then a hydrothermal reaction was carried out at 175°C for 10 h. After cooling, the nanospheres were centrifuged and washed, and then carbonized at 700°C in an Ar atmosphere for 3 h to obtain SiO2@C core-shell nanospheres. (3) Cobalt vanadium sulfide precursor loading: SiO2@C core-shell nanospheres were dispersed in deionized water, and CoCl2·6H2O and VCl3 were added, wherein the concentration of CoCl2·6H2O and VCl3 was 4:1. After stirring at 400 r / min for 1.5 h to homogenize, urea and thioacetamide were added and stirring was continued to obtain a mixed solution. (4) Hydrothermal sulfidation and template etching: The mixture in step (3) was subjected to hydrothermal sulfidation reaction at 90°C for 24 hours. After cooling, the precipitate was collected by centrifugation and soaked in etchant of 0.7 mol / L sodium hydroxide solution for 12 hours to obtain the etched precipitate. (5) Post-treatment: The etched precipitate was washed four times with deionized water and ethanol alternately, and then vacuum dried for 20 h under vacuum conditions of -0.09 MPa and 70 °C. After grinding, cobalt vanadium sulfide with egg yolk-shell structure was obtained @ hollow carbon nanospheres.

[0046] Example 3 (1) Preparation of SiO2 nanosphere template: Tetraethyl orthosilicate, ammonia, ethanol and deionized water were mixed, stirred at 40°C for 3 h and centrifuged and washed, and then dried at 80°C to obtain SiO2 nanospheres with a particle size of 200 nm. (2) Carbon coating: SiO2 nanospheres were dispersed in a 15% glucose aqueous solution with a mass ratio of 1:3. Urea was added, and then a hydrothermal reaction was carried out at 180°C for 9 hours. After cooling, the nanospheres were centrifuged and washed, and then carbonized at 800°C for 2.5 hours under an Ar atmosphere to obtain SiO2@C core-shell nanospheres. (3) Cobalt vanadium sulfide precursor loading: SiO2@C core-shell nanospheres were dispersed in deionized water, and CoCl2·6H2O and VCl3 were added, with the concentration of CoCl2·6H2O and VCl3 being 5:1. After stirring at 500 r / min for 1 h to achieve uniformity, urea and thioacetamide were added, and stirring was continued to obtain a mixed solution. (4) Hydrothermal sulfidation and template etching: The mixture from step (3) was subjected to hydrothermal sulfidation reaction at 160°C for 9 hours. After cooling, the precipitate was collected by centrifugation and soaked in 2 mol / L hydrofluoric acid solution for 8 hours to obtain the etched precipitate. (5) Post-treatment: The etched precipitate was washed 5 times with deionized water and ethanol alternately, and then vacuum dried for 15 h under vacuum conditions of -0.1 MPa and 80 °C. After grinding, cobalt vanadium sulfide with egg yolk-shell structure was obtained @ hollow carbon nanospheres.

[0047] Comparative Example (1) Take 0.5 mmol CoCl2·6H2O and 0.5 mmol VCl3 (molar ratio 1:1, to form a control with the cobalt-vanadium ratio in Examples 1-3), add them to deionized water, and stir well; (2) Add 15 mmol urea and 2.5 mmol thioacetamide (TAA), and continue stirring for 1 hour to obtain a mixture; (3) Transfer the mixture to a polytetrafluoroethylene reactor and hydrothermally react at 120°C for 24 hours; (4) After cooling, the mixture was filtered through a 0.45 μm polyethersulfone membrane, washed three times alternately with deionized water and ethanol, dried at 65 °C for 24 h, and ground to obtain a single cobalt vanadium sulfide (CoS). 1.097 ( / V7S8), with a morphology of stacked nanoflowers.

[0048] Performance testing The electrochemical performance was tested at room temperature (25°C) using a constant current charge-discharge test at 500 mA·g. -1 2A·g -1 The current density test measures the initial charge-discharge capacity and cycle performance. The coulombic efficiency is calculated by the charge-discharge capacity ratio. The structural stability test involves disassembling the coin cell after 200 cycles, removing the working electrode, cleaning it with deionized water / ethanol, vacuum drying it, observing the morphology of the active material and the integrity of the carbon shell, and statistically analyzing the carbon shell integrity rate. The testing was conducted in accordance with the following national standards: GB / T 31484-2015 "Negative Electrode Materials for Lithium-ion Batteries" (Reference Adaptation for Sodium-ion Battery Testing) and GB / T 31486-2015 "Test Methods for Discharge Performance of Lithium-ion Batteries"; general electrochemical testing specifications: three-electrode system testing standards and industry practices for coin cell assembly and performance testing; and material structure characterization standards: GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" and GB / T 13221-2004 "Determination of Particle Size Distribution of Nanopowders by Transmission Electron Microscopy". A coin cell battery was used, with the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres prepared in Examples 1-3 and the single cobalt vanadium sulfide prepared in the comparative example as electrodes, and a sodium metal sheet as the counter electrode. The performance test results of the products described in Examples 1-3 and the comparative example are shown in Table 1 below: Table 1 Performance test results of the products described in Examples 1-3 and the comparative examples

[0049] In summary, compared to the single cobalt vanadium sulfide prepared in the comparative example, the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres prepared in Examples 1-3 of this invention exhibit a 6.0%-7.3% increase in initial discharge capacity due to the enhanced conductivity of the carbon shell. Furthermore, the capacity decay under high current is slower, with the retention rate increasing from 45.0% to 72.0%-82.0% after 200 cycles and from 25.0% to 80.0%-85.0% after 1000 high-current cycles. The reserved voids in the egg yolk-shell structure buffer volume expansion, and the carbon shell inhibits material pulverization. The coulombic efficiency is improved to over 99.3%, and the carbon shell effectively blocks polysulfide shuttle, solving the irreversible capacity loss problem present in the comparative example. Moreover, the carbon shell integrity rate is ≥92%, completely resolving the core pain point of structural collapse in existing technologies.

[0050] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is determined by the appended claims.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure, characterized in that, It has an egg yolk-shell structure, wherein the egg yolk is a cobalt vanadium sulfide, the shell in the egg yolk-shell structure is a hollow carbon nanosphere, and a reserved gap is formed between the egg yolk and the shell.

2. The cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 1, characterized in that, The composition of the cobalt vanadium sulfide is CoS 1.097 A mixture of Co and V7S8, with a particle size of 50-100 nm. 2+ With V 3+ The molar ratio is 1~5:

1.

3. The cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 1, characterized in that, The thickness of the hollow carbon nanospheres is 10~30nm; the width of the reserved gaps is 30~80nm.

4. A method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Preparation of SiO2 nanosphere template: Tetraethyl orthosilicate, ammonia, ethanol and deionized water were mixed, stirred evenly and washed by centrifugation and then dried to obtain SiO2 nanospheres; (2) Carbon coating: SiO2 nanospheres were dispersed in an aqueous solution of carbon source, urea was added, and then a hydrothermal reaction was carried out. After cooling, the nanospheres were centrifuged and washed, and then carbonized under an Ar atmosphere to obtain SiO2@C core-shell nanospheres. (3) Cobalt vanadium sulfide precursor loading: SiO2@C core-shell nanospheres were dispersed in deionized water, CoCl2·6H2O and VCl3 were added, and after stirring evenly, urea and thioacetamide were added and stirring was continued to obtain a mixed solution; (4) Hydrothermal sulfidation and template etching: The mixture from step (3) is subjected to hydrothermal sulfidation reaction, cooled and centrifuged to collect the precipitate, and soaked in etching agent to obtain the etched precipitate; (5) Post-treatment: The etched precipitate was washed with deionized water and ethanol alternately 3 to 5 times, vacuum dried, and ground to obtain egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres.

5. The method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 4, characterized in that, The stirring parameters in step (1) are: temperature 25~40℃, time 2~6h; the drying temperature is 60~80℃; and the particle size of the SiO2 nanospheres is 100~200nm.

6. The method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 4, characterized in that, The carbon source aqueous solution in step (2) is glucose or sucrose, and the mass concentration of the carbon source aqueous solution is 5%~15%; the mass ratio of the carbon source to urea is 1:2~5; the mass ratio of the carbon source to SiO2 nanospheres is 1:1~3; the hydrothermal reaction parameters are: temperature 160~180℃, time 8~12h; the carbonization parameters are: temperature 600~800℃, time 2~4h.

7. The method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 4, characterized in that, The total molar amount of CoCl2·6H2O and VCl3 mentioned in step (3) is 1 mmol, and Co 2+ and V 3+ The molar ratio of urea to Co is 1~5:1; 2+ The molar ratio of the thioacetamide to Co is 10~50:1; 2+ The molar ratio is 1~10:1; the stirring parameters are: rotation speed 300~500 r / min, time 0.5~2 h.

8. The method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 4, characterized in that, The hydrothermal sulfidation reaction parameters in step (4) are: temperature 80~160℃, time 8~24h; the etching agent is 0.5~2mol / L hydrofluoric acid solution or sodium hydroxide solution; the soaking is 6~12h.

9. The method for preparing a cobalt vanadium sulfide@hollow carbon nanosphere with an egg yolk-shell structure according to claim 4, characterized in that, The vacuum drying parameters in step (5) are: vacuum degree -0.08~-0.1MPa, temperature 60~80℃, and time 12~24h.

10. An application of the egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres as described in claim 1, characterized in that, The specific application is the use of egg yolk-shell structured cobalt vanadium sulfide@hollow carbon nanospheres in the preparation of sodium-ion battery anode materials.

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