A nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, its preparation method and application

Abstract

This invention relates to the field of next-generation energy storage, and discloses a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, its preparation method, and its application. The method includes: dissolving ammonium metavanadate and cobalt salt in ethanol, adding thioacetamide, mixing thoroughly, and then placing the mixture in a reactor for high-temperature and high-pressure reaction to obtain Co-doped VS4 material Co-VS4; depositing a dense nitrogen-doped carbon layer on the surface of Co-VS4 using chemical vapor deposition, with acetylene as the carbon source and acetonitrile as the nitrogen source; and calcining the Co-VS4 with the dense nitrogen-doped carbon layer in a tube furnace by introducing active gas to create pores, thus obtaining the nitrogen-doped carbon-coated cobalt vanadium sulfide composite material. This invention, through the synergistic effect of cobalt doping, dense nitrogen-doped carbon coating, and active gas pore creation, effectively alleviates volume expansion and improves electron and ion transport efficiency, enabling the composite material to exhibit high specific capacity, excellent cycle stability, and rate performance as a sodium-ion battery anode.

Description

Technical Field

[0001] This invention relates to the field of next-generation energy storage, and more specifically, to a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries are considered one of the most promising next-generation rechargeable batteries for large-scale energy storage and low-speed electric vehicles due to the abundance and low cost of sodium resources and their similarity in working principle to lithium-ion batteries. However, the ionic radius of sodium ions is significantly larger than that of lithium ions, resulting in slow insertion / extraction kinetics in electrode materials, low reversible capacity, and large irreversible capacity loss. Therefore, developing high-performance anode materials has become crucial for the practical application of sodium-ion batteries. Based on the sodium storage mechanism, anode materials can be classified into intercalation-type (such as carbon materials), alloy-type (such as tin, antimony, etc.), and conversion-type (such as metal oxides, sulfides, selenides). Among them, conversion-type transition metal sulfides have attracted widespread attention due to their high theoretical specific capacity, abundant redox sites, and superior conductivity and narrower band gap compared to metal oxides.

[0003] Cobalt-vanadium bimetallic sulfides, as an important class of conversion materials, hold promise for achieving faster charge transfer and more stable cycling performance than monometallic sulfides by utilizing the synergistic coordination effect between cobalt and vanadium. However, existing cobalt-vanadium sulfide-based anode materials still suffer from the following major drawbacks in practical applications: (1) Volume expansion problem: Cobalt vanadium sulfide undergoes a conversion reaction during charge and discharge, producing metal nanoparticles and sodium sulfide, accompanied by significant volume changes (usually exceeding 100%). This drastic volume expansion can lead to the pulverization of electrode materials, detachment from the current collector, and repeated rupture and regeneration of the solid electrolyte interphase (SEI) film, ultimately resulting in rapid capacity decay and poor cycle stability.

[0004] (2) Insufficient conductivity: Although bimetallic sulfides are an improvement over monometallic sulfides, their overall electronic conductivity is still low, making it difficult to meet the rate performance requirements at high current densities. At the same time, the small diffusion coefficient of sodium ions in the sulfide lattice limits their fast charging capability.

[0005] (3) Limitations of existing carbon coating technology: To alleviate the above problems, researchers often adopt carbon material coating strategies. However, existing carbon coating layers are mostly dense structures. On the one hand, the mechanical flexibility of dense carbon layers is limited, which cannot effectively buffer the volume expansion and contraction of active materials during repeated sodium insertion / extraction processes. On the other hand, dense carbon layers hinder the wetting of electrolyte into internal active materials and also limit the rapid transport of sodium ions. In addition, the interfacial bonding strength between ordinary carbon layers and metal sulfides is weak, and peeling is prone to occur during long-term cycling.

[0006] (4) Insufficient control over pore structure and doping: Nitrogen-doped carbon materials have been shown to enhance sodium ion adsorption capacity and electronic conductivity by introducing defect sites. However, existing preparation techniques have limited ability to control the pore structure of carbon layers, making it difficult to simultaneously achieve high specific surface area, interconnected ion diffusion channels, and sufficient mechanical buffer space. Some studies have attempted to create pores using the hard template method, but this method has drawbacks such as complex processes, high costs, and incomplete template removal, which are not conducive to large-scale production.

[0007] In summary, existing technologies lack a cobalt-vanadium sulfide-based anode material that can effectively buffer volume expansion, provide a fast ion / electron transport channel, and exhibit strong interfacial bonding. Therefore, developing a cobalt-vanadium sulfide composite material with a porous nitrogen-doped carbon shell coating structure is of great significance for improving the cycle stability and rate performance of sodium-ion batteries. Summary of the Invention

[0008] In view of this, the present invention proposes a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, its preparation method and application, aiming to solve the problems of volume expansion and poor conductivity of cobalt vanadium sulfide-based anode materials in the current technology.

[0009] This invention proposes a method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, comprising the following steps: 1) Ammonium metavanadate and cobalt salt were dissolved in ethanol, and then thioacetamide was added and mixed evenly. The mixture was then placed in a reaction vessel for high temperature and high pressure reaction to obtain Co-doped VS4 material Co-VS4. 2) A dense nitrogen-doped carbon layer was deposited on the Co-VS4 surface using chemical vapor deposition with acetylene as the carbon source and acetonitrile as the nitrogen source; 3) Co-VS4 with a dense nitrogen-doped carbon layer on its surface is placed in a tube furnace and active gas is introduced for calcination to create pores, thus obtaining a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0010] Preferably, the ratio of ammonium metavanadate, ethanol and thioacetamide used in step 1) is 0.1 mol: 10~20 mL: 0.4~0.6 mol; The cobalt salt includes one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate; The molar ratio of vanadium in the ammonium metavanadate to cobalt in the cobalt salt is 1:0.01~0.1.

[0011] Preferably, the high-temperature and high-pressure reaction in step 1) is carried out at a temperature of 170~190℃ for 20~28h.

[0012] Preferably, the temperature of the chemical vapor deposition in step 2) is 700~800℃, the time is 30~60min, the pressure is 10~30kPa, and the carrier gas is hydrogen. In the chemical vapor deposition process, the molar ratio of acetylene, acetonitrile and carrier gas is 1:0.1~0.2:8~9, and the gas flow rate is 0.01~0.05m / s.

[0013] Preferably, the active gas in step 3) is water vapor or carbon dioxide; The calcination temperature is 800~950℃, and the calcination time is 4~6h.

[0014] Preferably, inert gas is used as diluent gas during the introduction of the active gas in step 1); The ratio of the active gas to the inert gas is 0.01~0.05:1; Using a standard atmospheric barometer, the introduction velocity of the active and inert gases is 0.5~1m. 3 / h.

[0015] This invention provides a method for preparing nitrogen-doped carbon-coated cobalt vanadium sulfide composite materials.

[0016] This invention provides an application of nitrogen-doped carbon-coated cobalt vanadium sulfide composite material in the preparation of sodium-ion battery anode materials.

[0017] The present invention provides a sodium-ion battery negative electrode sheet, the negative electrode sheet comprising a current collector and a coating material disposed on the surface of the current collector, the coating material comprising the above-mentioned nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0018] The present invention provides a sodium-ion battery, including the above-mentioned negative electrode sheet.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a high-temperature, high-pressure reaction to dope Co into VS4, utilizing the synergistic coordination effect between cobalt and vanadium to generate more electrochemical active sites in the material. The cobalt doping also alters the electronic structure of VS4, lowering the reaction energy barrier during sodium ion insertion / extraction, thereby enhancing the material's sodium storage capacity and further improving the battery's reversible specific capacity.

[0020] During charge and discharge, cobalt vanadium sulfide undergoes an electrochemical reaction, generating sodium sulfide, and the volume of Co-VS4 changes drastically. This invention first uses chemical vapor deposition to form a dense nitrogen-doped carbon coating layer. This dense layer bonds firmly to the interface of the active material, effectively constraining the volume expansion of the active material and preventing electrode pulverization and detachment. Subsequently, pores are created on the surface of the dense carbon layer using an active gas. These pores not only provide channels for electrolyte wetting but, more importantly, act as volume buffer spaces, accommodating localized volume changes of the active material during sodium intercalation / deintercalation. Compared to a simple dense carbon layer, this "dense inner layer + porous outer layer" structure avoids stress concentration caused by excessive rigidity of the carbon layer; compared to simple porous carbon, the dense inner layer ensures the integrity of the electron conduction path and interface stability. The synergistic effect of these two elements allows the electrode to maintain structural integrity during long-term cycling, significantly improving capacity retention.

[0021] The dense nitrogen-doped carbon layer itself possesses excellent electronic conductivity, and the defect sites introduced by nitrogen doping enhance the adsorption capacity of the carbon layer for sodium ions, accelerating charge transfer. Simultaneously, the formation of surface pores shortens the diffusion distance of sodium ions from the electrolyte to the surface of the active material, providing a rapid ion diffusion channel. Therefore, electrons can be rapidly conducted to the active center through the dense carbon layer, while sodium ions rapidly enter and diffuse through the surface pores. The combined effect significantly reduces ohmic polarization and concentration polarization of the battery, enabling the composite material to maintain high capacity even at high current densities, resulting in a significant improvement in rate performance.

[0022] This application employs chemical vapor deposition to form a carbon layer, followed by pore creation using an active gas, avoiding the cumbersome steps and contamination issues associated with subsequent template removal in the hard template method. Water vapor and carbon dioxide are inexpensive and readily available pore-forming agents. By adjusting the gas concentration, processing temperature, and time, the number and size of pores can be precisely controlled, achieving adjustable porosity of the carbon layer. The entire process is simple, environmentally friendly, and low-cost, easily scalable for production, and has promising prospects for industrialization. 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 proposes a method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, comprising the following steps: 1) Ammonium metavanadate and cobalt salt were dissolved in ethanol, and then thioacetamide was added and mixed evenly. The mixture was then placed in a reaction vessel for high temperature and high pressure reaction to obtain Co-doped VS4 material Co-VS4. 2) A dense nitrogen-doped carbon layer was deposited on the Co-VS4 surface using chemical vapor deposition with acetylene as the carbon source and acetonitrile as the nitrogen source; 3) Co-VS4 with a dense nitrogen-doped carbon layer on its surface is placed in a tube furnace and active gas is introduced for calcination to create pores, thus obtaining a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0029] In this invention, the ratio of ammonium metavanadate, ethanol and thioacetamide in step 1) is 0.1 mol: 10~20 mL: 0.4~0.6 mol, preferably 0.1 mol: 11~19 mL: 0.42~0.58 mol, more preferably 0.1 mol: 12~18 mL: 0.45~0.55 mol, and even more preferably 0.1 mol: 13~17 mL: 0.48~0.52 mol.

[0030] In this invention, the cobalt salt includes one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate.

[0031] In this invention, the molar ratio of vanadium in the ammonium metavanadate to cobalt in the cobalt salt is 1:0.01~0.1, preferably 1:0.03~0.08, more preferably 1:0.04~0.07, and even more preferably 1:0.05~0.06.

[0032] In this invention, the temperature of the high-temperature and high-pressure reaction in step 1) is 170~190℃, preferably 175~185℃, more preferably 178~182℃, and even more preferably 180℃; the time is 20~28h, preferably 22~26h, more preferably 23~25h, and even more preferably 24~25h.

[0033] In this invention, the temperature of the chemical vapor deposition in step 2) is 700-800°C, preferably 720-780°C, more preferably 740-760°C, and even more preferably 745-755°C; the time is 30-60 min, preferably 35-55 min, more preferably 40-50 min, and even more preferably 43-47 min; the pressure is 10-30 kPa, preferably 15-25 kPa, more preferably 18-22 kPa, and even more preferably 19-21 kPa; and the carrier gas is hydrogen. A pressure lower than atmospheric pressure is beneficial for forming a uniform and dense coating layer.

[0034] In this invention, the molar ratio of acetylene, acetonitrile and carrier gas in the chemical vapor deposition process is 1:0.1~0.2:8~9, preferably 1:0.12~0.18:8.2~8.8, more preferably 1:0.14~0.16:8.4~8.6, and even more preferably 1:0.15~0.16:8.5~8.6; the gas flow rate is 0.01~0.05m / s, preferably 0.02~0.04m / s, more preferably 0.025~0.035m / s, and even more preferably 0.03~0.035m / s.

[0035] In this invention, the active gas in step 3) is water vapor or carbon dioxide.

[0036] In this invention, the calcination temperature is 800~950℃, preferably 830~920℃, more preferably 860~890℃, and even more preferably 870~880℃; the calcination time is 4~6h, preferably 4.5~5.5h, more preferably 4.8~5.2h, and even more preferably 5h.

[0037] In this invention, an inert gas is used as a diluent during the introduction of the active gas in step 1).

[0038] In this invention, the ratio of the active gas to the inert gas is 0.01~0.05:1, preferably 0.02~0.04:1, more preferably 0.025~0.035:1, and even more preferably 0.03~0.035:1.

[0039] Using a standard atmospheric barometer, the introduction velocity of the active and inert gases is 0.5~1m. 3 / h, preferably 0.6~0.9m 3 / h, further preferably 0.7~0.85m 3 / h, more preferably 0.75~0.8m 3 / h.

[0040] This invention provides a method for preparing nitrogen-doped carbon-coated cobalt vanadium sulfide composite materials.

[0041] This invention provides an application of nitrogen-doped carbon-coated cobalt vanadium sulfide composite material in the preparation of sodium-ion battery anode materials.

[0042] The present invention provides a sodium-ion battery negative electrode sheet, the negative electrode sheet comprising a current collector and a coating material disposed on the surface of the current collector, the coating material comprising the above-mentioned nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0043] The present invention provides a sodium-ion battery, including the above-mentioned negative electrode sheet.

[0044] Example 1 1) Weigh out ammonium metavanadate, cobalt salt, ethanol, and thioacetamide according to the following proportions: the ratio of ammonium metavanadate, ethanol, and thioacetamide is 0.1 mol: 10 mL: 0.5 mol. The cobalt salt is cobalt nitrate, and the molar ratio of vanadium in ammonium metavanadate to cobalt in the cobalt salt is 1:0.05. Dissolve ammonium metavanadate and cobalt salt in ethanol and stir until completely dissolved. Add thioacetamide and continue stirring for 30 minutes until homogeneous. Transfer the mixture to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven. Maintain a high-temperature and high-pressure reaction at 180°C for 24 hours. After the reaction, allow it to cool naturally to room temperature. Centrifuge the reaction product and wash it three times alternately with ethanol and deionized water, centrifuging for 10 minutes after each wash. After washing, place it in a vacuum drying oven and dry it at 120°C for 8 hours to obtain Co-doped VS4 material (Co-VS4).

[0045] 2) Deposition of a dense nitrogen-doped carbon layer on the surface of Co-VS4 using chemical vapor deposition: The Co-VS4 powder prepared in step 1) was uniformly spread in a quartz boat and placed in a tube furnace. First, a carrier gas (hydrogen) was introduced to purge the air in the furnace for 20 minutes to remove the air. Then, the temperature was raised to 800℃, the pressure in the furnace was controlled at 25 kPa, and the gas flow rate was adjusted to 0.03 m / s. A mixture of acetylene (carbon source), acetonitrile (nitrogen source), and carrier gas (hydrogen) was introduced, wherein the molar ratio of acetylene, acetonitrile, and carrier gas was 1:0.1:8. Chemical vapor deposition was carried out under these conditions for 40 minutes. After the deposition was completed, the introduction of acetylene and acetonitrile was stopped, the carrier gas was continued to be introduced, and the mixture was naturally cooled to room temperature to obtain Co-VS4 with a dense nitrogen-doped carbon layer on the surface.

[0046] 3) Calcination to create pores: The Co-VS4 with a dense nitrogen-doped carbon layer obtained in step 2) is placed in a tube furnace. An inert gas is used as a dilution gas, and an active gas (water vapor or carbon dioxide) is introduced, with the ratio of active gas to inert gas being 0.02:1. The introduction rate of the active gas and inert gas is 0.5 m / s (using a standard atmospheric pressure gauge). 3 / h; control the temperature of the tube furnace to 900℃ and maintain this temperature for 5h; after calcination, stop the flow of active gas, continue to flow inert gas, and cool to room temperature to obtain nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0047] Example 2 1) Weigh out ammonium metavanadate, cobalt salt, ethanol, and thioacetamide according to the following proportions: the ratio of ammonium metavanadate, ethanol, and thioacetamide is 0.1 mol: 20 mL: 0.6 mol. The cobalt salt is cobalt chloride, and the molar ratio of vanadium in ammonium metavanadate to cobalt in the cobalt salt is 1:0.03. Dissolve ammonium metavanadate and cobalt salt in ethanol and stir until completely dissolved. Add thioacetamide and continue stirring for 30 minutes until homogeneous. Transfer the mixture to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven. Maintain a high-temperature and high-pressure reaction at 190°C for 20 hours. After the reaction, allow it to cool naturally to room temperature. Centrifuge the reaction product and wash it three times alternately with ethanol and deionized water, centrifuging for 15 minutes after each wash. After washing, place it in a vacuum drying oven and dry it at 120°C for 10 hours to obtain Co-doped VS4 material (Co-VS4).

[0048] 2) Deposition of a dense nitrogen-doped carbon layer on the surface of Co-VS4 using chemical vapor deposition: The Co-VS4 powder prepared in step 1) was uniformly spread in a quartz boat and placed in a tube furnace. First, a carrier gas (hydrogen) was introduced to purge the air in the furnace for 20 minutes to remove the air. Then, the temperature was raised to 740℃, the pressure in the furnace was controlled at 30 kPa, and the gas flow rate was adjusted to 0.04 m / s. A mixture of acetylene (carbon source), acetonitrile (nitrogen source), and carrier gas (hydrogen) was introduced, wherein the molar ratio of acetylene, acetonitrile, and carrier gas was 1:0.15:8.5. Chemical vapor deposition was carried out under these conditions for 30 minutes. After the deposition was completed, the introduction of acetylene and acetonitrile was stopped, the carrier gas was continued to be introduced, and the mixture was naturally cooled to room temperature to obtain Co-VS4 with a dense nitrogen-doped carbon layer on the surface.

[0049] 3) Calcination to create pores: The Co-VS4 with a dense nitrogen-doped carbon layer obtained in step 2) is placed in a tube furnace. An inert gas is used as a dilution gas, and an active gas (water vapor or carbon dioxide) is introduced, with the ratio of active gas to inert gas being 0.05:1. The introduction rate of the active gas and inert gas is 0.8 m / s (using a standard atmospheric pressure gauge). 3 / h; control the tube furnace to heat up to 950℃ and maintain this temperature for calcination for 4h; after calcination, stop the flow of active gas, continue to flow inert gas, and cool to room temperature to obtain nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0050] Example 3 1) Weigh out ammonium metavanadate, cobalt salt, ethanol, and thioacetamide according to the following proportions: the ratio of ammonium metavanadate, ethanol, and thioacetamide is 0.1 mol: 15 mL: 0.6 mol. The cobalt salt is cobalt chloride, and the molar ratio of vanadium in ammonium metavanadate to cobalt in the cobalt salt is 1:0.08. Dissolve ammonium metavanadate and cobalt salt in ethanol and stir until completely dissolved. Add thioacetamide and continue stirring for 20 minutes until homogeneous. Transfer the mixture to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven. Maintain a high-temperature and high-pressure reaction at 175°C for 25 hours. After the reaction, allow it to cool naturally to room temperature. Centrifuge the reaction product and wash it three times alternately with ethanol and deionized water, centrifuging for 15 minutes after each wash. After washing, place it in a vacuum drying oven and dry it at 120°C for 8 hours to obtain Co-doped VS4 material (Co-VS4).

[0051] 2) Deposition of a dense nitrogen-doped carbon layer on the surface of Co-VS4 using chemical vapor deposition: The Co-VS4 powder prepared in step 1) was uniformly spread in a quartz boat and placed in a tube furnace. First, a carrier gas (hydrogen) was introduced to purge the air in the furnace for 20 minutes to remove the air. Then, the temperature was raised to 780℃, the pressure in the furnace was controlled at 15 kPa, and the gas flow rate was adjusted to 0.05 m / s. A mixture of acetylene (carbon source), acetonitrile (nitrogen source), and carrier gas (hydrogen) was introduced, wherein the molar ratio of acetylene, acetonitrile, and carrier gas was 1:0.1:9. Chemical vapor deposition was carried out under these conditions for 55 minutes. After the deposition was completed, the introduction of acetylene and acetonitrile was stopped, the carrier gas was continued to be introduced, and the mixture was naturally cooled to room temperature to obtain Co-VS4 with a dense nitrogen-doped carbon layer on the surface.

[0052] 3) Calcination to create pores: The Co-VS4 with a dense nitrogen-doped carbon layer obtained in step 2) is placed in a tube furnace. An inert gas is used as a dilution gas, and an active gas (water vapor or carbon dioxide) is introduced, wherein the ratio of active gas to inert gas is 0.025:1. The introduction rate of active gas and inert gas is 0.8 m / s (using a standard atmospheric pressure gauge). 3 / h; control the tube furnace to heat up to 920℃ and maintain this temperature for calcination for 6h; after calcination, stop the flow of active gas, continue to flow inert gas, and cool to room temperature to obtain nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0053] Example 4 1) Weigh out ammonium metavanadate, cobalt salt, ethanol, and thioacetamide according to the following proportions: the ratio of ammonium metavanadate, ethanol, and thioacetamide is 0.1 mol: 18 mL: 0.55 mol. The cobalt salt is cobalt nitrate, and the molar ratio of vanadium in ammonium metavanadate to cobalt in the cobalt salt is 1:0.08. Dissolve ammonium metavanadate and cobalt salt in ethanol and stir until completely dissolved. Add thioacetamide and continue stirring for 20 minutes until homogeneous. Transfer the mixture to a polytetrafluoroethylene-lined reactor, seal it, and place it in an oven. Maintain a high-temperature and high-pressure reaction at 170°C for 28 hours. After the reaction, allow it to cool naturally to room temperature. Centrifuge the reaction product and wash it three times alternately with ethanol and deionized water, centrifuging for 15 minutes after each wash. After washing, place it in a vacuum drying oven and dry it at 100°C for 12 hours to obtain Co-doped VS4 material (Co-VS4).

[0054] 2) Deposition of a dense nitrogen-doped carbon layer on the surface of Co-VS4 using chemical vapor deposition: The Co-VS4 powder prepared in step 1) was uniformly spread in a quartz boat and placed in a tube furnace. First, a carrier gas (hydrogen) was introduced to purge the air in the furnace for 20 minutes to remove the air. Then, the temperature was raised to 755℃, the pressure in the furnace was controlled at 22 kPa, and the gas flow rate was adjusted to 0.035 m / s. A mixture of acetylene (carbon source), acetonitrile (nitrogen source), and carrier gas (hydrogen) was introduced, wherein the molar ratio of acetylene, acetonitrile, and carrier gas was 1:0.15:8.5. Chemical vapor deposition was carried out under these conditions for 47 minutes. After the deposition was completed, the introduction of acetylene and acetonitrile was stopped, the carrier gas was continued to be introduced, and the mixture was naturally cooled to room temperature to obtain Co-VS4 with a dense nitrogen-doped carbon layer on the surface.

[0055] 3) Calcination to create pores: The Co-VS4 with a dense nitrogen-doped carbon layer obtained in step 2) is placed in a tube furnace. An inert gas is used as a dilution gas, and an active gas (water vapor or carbon dioxide) is introduced, with the ratio of active gas to inert gas being 0.03:1. The introduction rate of the active gas and inert gas is 0.75 m / s (using a standard atmospheric pressure gauge). 3 / h; control the tube furnace to heat up to 880℃ and maintain this temperature for calcination for 4.5h; after calcination, stop the flow of active gas, continue to flow inert gas, and cool to room temperature to obtain nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

[0056] Comparative Example 1 Example 1 Step 1) The Co-doped VS4 material (Co-VS4) was prepared.

[0057] Comparative Example 2 Example 1, step 2): The Co-VS4 with a dense nitrogen-doped carbon layer on the surface was prepared.

[0058] The composite materials prepared in Examples 1-4 and Comparative Examples 1-2 were used for the assembly of sodium-ion batteries, and their electrochemical performance was tested. The specific assembly methods, testing methods, and test results are as follows: (1) Preparation of the negative electrode sheet for sodium-ion batteries: The active material (the composite material prepared in Examples 1-4 and Comparative Examples 1-2) was mixed with a conductive agent (conductive carbon black) and a binder (PVDF polyvinylidene fluoride) at a mass ratio of 5:2:1. The mixture was then coated onto the surface of the current collector (an 80 μm thick aluminum foil) at a coating weight of 0.03 mg / cm². 2 Then it is placed in a roller press (pressure of 10MPa) and pressed for 30 minutes, and finally dried in an oven at 100℃ for 24 hours to obtain the negative electrode sheet of sodium ion battery.

[0059] (2) Assembly of sodium-ion batteries: A sodium-ion battery is assembled using coin cell half-cells, with a sodium metal sheet serving as the counter electrode. The assembly sequence is as follows: Positive electrode shell → prepared electrode sheet → separator → sodium sheet → gasket → spring sheet → negative electrode shell; Assembly is carried out in the glove box.

[0060] (3) Sodium-ion battery performance testing: 1. Place it at room temperature and perform constant current charge and discharge at a current density of 500 mAg. -1 Calculate its initial discharge specific capacity and discharge specific capacity after 100 constant current charge-discharge cycles.

[0061] 2. Test the battery at 2A·g -1 The discharge capacity after 500 cycles at a high current density.

[0062] The test results are shown in Table 1.

[0063] Table 1. Electrochemical performance test results of sodium-ion batteries prepared using the active materials described in Examples 1-4 and Comparative Examples 1-2.

[0064] As can be seen from the data in Table 1, at 500 mA·g -1 After 100 cycles at a current density, the discharge specific capacity of the nitrogen-doped carbon-coated cobalt vanadium sulfide composite materials obtained in Examples 1-4 of this invention still reached 722.95-738.57 mAh·g. -1 Capacity retention rate of 77%~79%, at 2A·g -1 It can still maintain 302.18~408.29 mAh·g after 500 cycles under high current. -1 The high capacity of pure Co-VS4 (Comparative Example 1) is only 487.96 mAh·g after 100 cycles. -1 The retention rate was approximately 59%, and the capacity of the dense nitrogen-doped carbon-coated, non-porous Co-VS4 (Comparative Example 2) was only 246.72 mAh·g after 100 cycles. -1The retention rate is as low as 36%, and the capacity after long-term high-current cycling is also far lower than that of the example. From the perspective of principle and beneficial effects, the present invention optimizes the electronic structure of the material by cobalt doping, enhances the active sites and reaction kinetics, and then forms a dense nitrogen-doped carbon layer that is firmly bonded to the active material by chemical vapor deposition. This effectively constrains the volume expansion during charging and discharging, prevents electrode pulverization and detachment, and ensures continuous electron conduction. Combined with the pore-forming structure of water vapor / carbon dioxide active gas calcination, a "dense inner layer + porous outer layer" structure is constructed. This provides electrolyte wetting and rapid sodium ion transport channels, and also provides buffer space for volume changes and avoids stress concentration. Thus, it significantly suppresses capacity decay, greatly improves cycle stability and long-term cycle capacity retention. Its cycle performance is far superior to pure Co-VS4 without carbon coating and the comparative sample with only dense coating and no pores.

[0065] 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 method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material, characterized in that, Includes the following steps: 1) Ammonium metavanadate and cobalt salt were dissolved in ethanol, and then thioacetamide was added and mixed evenly. The mixture was then placed in a reaction vessel for high temperature and high pressure reaction to obtain Co-doped VS4 material Co-VS4. 2) A dense nitrogen-doped carbon layer was deposited on the Co-VS4 surface using chemical vapor deposition with acetylene as the carbon source and acetonitrile as the nitrogen source; 3) Co-VS4 with a dense nitrogen-doped carbon layer on its surface is placed in a tube furnace and active gas is introduced for calcination to create pores, thus obtaining a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material.

2. The method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material according to claim 1, characterized in that, In step 1), the ratio of ammonium metavanadate, ethanol, and thioacetamide is 0.1 mol: 10-20 mL: 0.4-0.6 mol. The cobalt salt includes one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate; The molar ratio of vanadium in the ammonium metavanadate to cobalt in the cobalt salt is 1:0.01~0.

1.

3. The method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material according to claim 1, characterized in that, The high-temperature and high-pressure reaction in step 1) is carried out at a temperature of 170~190℃ for 20~28h.

4. The method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material according to claim 1, characterized in that, The chemical vapor deposition in step 2) is carried out at a temperature of 700-800℃, a time of 30-60 min, a pressure of 10-30 kPa, and hydrogen as the carrier gas. In the chemical vapor deposition process, the molar ratio of acetylene, acetonitrile and carrier gas is 1:0.1~0.2:8~9, and the gas flow rate is 0.01~0.05m / s.

5. The method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material according to claim 1, characterized in that, The active gas mentioned in step 3) is water vapor or carbon dioxide; The calcination temperature is 800~950℃, and the calcination time is 4~6h.

6. The method for preparing a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material according to claim 5, characterized in that, In step 1), an inert gas is used as a diluent during the introduction of the active gas. The ratio of the active gas to the inert gas is 0.01~0.05:1; Using a standard atmospheric barometer, the introduction velocity of the active and inert gases is 0.5~1m. 3 / h.

7. The nitrogen-doped carbon-coated cobalt vanadium sulfide composite material prepared by the method according to any one of claims 1 to 6.

8. The application of the nitrogen-doped carbon-coated cobalt vanadium sulfide composite material according to claim 7 in the preparation of sodium-ion battery anode materials.

9. A sodium-ion battery negative electrode sheet, characterized in that, The negative electrode includes a current collector and a coating material disposed on the surface of the current collector, wherein the coating material includes a nitrogen-doped carbon-coated cobalt vanadium sulfide composite material as described in claim 7.

10. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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