A flexible lithium-sulfur battery positive electrode material containing a heterostructure material and a preparation method and application thereof

Abstract

This invention relates to the technical field of lithium-sulfur batteries, specifically to a method for preparing a flexible lithium-sulfur battery cathode material containing a heterostructure. First, a carbon source, niobium salt, and a pore-forming agent are dissolved in a solvent to obtain a spinning solution, which is then electrospun to obtain a first product. Second, the first product is dried, followed by pre-oxidation and pore-forming carbonization. The resulting second product is then mixed with selenium powder under a reducing atmosphere for selenization treatment to obtain a flexible electrode material. Finally, the flexible electrode material is subjected to sulfur loading treatment to obtain the lithium-sulfur battery cathode material containing the heterostructure. In the cathode material prepared by this invention, the Nb₂O₅-NbSe₂ heterostructure combined with porous carbon nanofibers exhibits adsorption and catalytic effects on lithium polysulfides in lithium-sulfur batteries. This effectively suppresses the "shuttle effect" of lithium polysulfides, promotes the reaction kinetics of lithium polysulfides, and significantly improves the energy density and cycle stability of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-sulfur batteries, specifically relating to a flexible lithium-sulfur battery cathode material containing heterostructure materials and its preparation method, as well as the application of the aforementioned flexible lithium-sulfur battery cathode material. Background Technology

[0002] Lithium-sulfur batteries are rechargeable batteries that use metallic lithium as the negative electrode and sulfur as the positive electrode. They have attracted widespread attention due to their extremely high theoretical capacity and energy density, as well as their environmental friendliness. Their working principle is based on the reversible redox reaction between sulfur (S) and lithium (Li₂S) to achieve charging and discharging. During discharge, solid sulfur is reduced to a series of soluble lithium polysulfides (Li₂S₂). n The lithium-sulfur battery process involves intermediates (Li₂S₈, Li₂S₆, and Li₂S₄), primarily including Li₂S₈, Li₂S₆, and Li₂S₄, which ultimately transform into insoluble Li₂S₂ / Li₂S. The charging process is the reverse. Soluble lithium polysulfides shuttle between the positive and negative electrodes with the electrolyte flow, diffusing towards the negative electrode and reacting directly with the metallic lithium. This results in the formation of Li₂S₂ / Li₂S deposits on the lithium negative electrode surface, blocking the transport channels for lithium ions and electrons, creating "dead sulfur" and causing irreversible degradation of the active material—this is the "shuttle effect." It reduces sulfur utilization and coulombic efficiency, causing rapid capacity decay and severely hindering the commercialization of lithium-sulfur batteries. Therefore, the "shuttle effect" is one of the key issues hindering the practical application of batteries. During discharge, the conversion of soluble polysulfides into the final Li₂S₂ / Li₂S requires overcoming a significant energy barrier, resulting in very poor reaction kinetics. Therefore, the poor reaction kinetics of polysulfides are the second key reason hindering the practical application of batteries.

[0003] To address the aforementioned issues, designing an ideal host material for sulfur loading requires not only a well-designed electrode structure with strong adsorption of polysulfides, but also high catalytic activity to promote polysulfide conversion reactions and accelerate Li₂S deposition / dissolution. Cai et al. found that CoSe₂ possesses excellent conductivity and catalytic performance; however, its weak interaction with polysulfides still leads to a "shuttle effect" and reduced cycle performance. Therefore, heterostructures combining strong adsorption and high catalytic activity are among the best host materials for improving lithium-sulfur battery performance. For example, the MoO₂ / Mo₃N₂ heterostructure proposed by Li et al. can achieve a synergistic promoting effect through the strong adsorption of MoO₂ and the high conductivity of Mo₃N₂, thus enhancing lithium-sulfur battery performance. Nevertheless, its low catalytic activity sites somewhat hinder its acceleration of polysulfide conversion reactions. Furthermore, the WS₂-WO₃ heterostructure prepared by Zhang et al. exhibits a good balance between adsorption and catalytic activity. However, its low conductivity necessitates the addition of a large amount of highly conductive additives, thus limiting the active sulfur loading in the electrode.

[0004] Furthermore, with the current popularization and promotion of flexible electronic devices and wearable electronic devices, flexible electrode materials are not only expected to be promoted and applied in the above-mentioned devices, but also have the advantage of high loading capacity when loading active materials.

[0005] Based on this, a flexible lithium-sulfur battery cathode material that can effectively solve the problems of "shuttle effect" and poor reaction kinetics faced by lithium-sulfur batteries is provided. This is of great significance for improving the electrochemical performance and cycle stability of lithium-sulfur batteries, as well as promoting the development and application of lithium-sulfur batteries in flexible electronic devices. It is also a technical problem that urgently needs to be solved. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing a flexible lithium-sulfur battery cathode material that can effectively solve the problems of "shuttle effect" and poor reaction kinetics faced by lithium-sulfur batteries.

[0007] The second objective of this invention is to provide a flexible lithium-sulfur battery cathode material that can effectively solve the problems of "shuttle effect" and poor reaction kinetics faced by lithium-sulfur batteries.

[0008] The third objective of this invention is to provide an application of a flexible lithium-sulfur battery cathode material containing heterostructure materials.

[0009] One of the technical solutions adopted by this invention to achieve its objective is to provide a method for preparing a flexible lithium-sulfur battery cathode material containing heterostructure materials, comprising the following steps:

[0010] S1. Dissolve carbon source, niobium salt and pore-forming agent in solvent to obtain spinning solution, and obtain the first product by electrospinning;

[0011] S2. The first product is dried, then pre-oxidized, and then placed in an inert atmosphere for pore-forming carbonization to obtain the second product.

[0012] S3. Under a reducing atmosphere, the second product is mixed with selenium powder for selenization treatment to obtain a flexible electrode material.

[0013] S4. The flexible electrode material is subjected to sulfur loading treatment to obtain a lithium-sulfur battery cathode material containing heterostructure material.

[0014] The overall concept of this invention is as follows:

[0015] This invention provides a lithium-sulfur battery cathode material with an Nb₂O₅-NbSe₂ heterostructure. The transition metal oxide Nb₂O₅ exhibits high polarity, forming a strong adsorption interaction with equally polar polysulfides, effectively adsorbing polysulfides as a sulfur host material. NbSe₂ significantly lowers the Li₂S nucleation energy barrier and enhances the redox reversibility between Li₂S and polysulfides. This invention combines the strong adsorption capacity of Nb₂O₅ with the good conductivity and catalytic activity of NbSe₂ to construct a host material with dual "adsorption-catalysis" functions, thus addressing the problems of "shuttle effect" and poor reaction kinetics faced by lithium-sulfur batteries.

[0016] Furthermore, in the preparation method of this invention, an Nb₂O₅-NbSe₂ heterostructure is embedded in N and Se co-doped porous carbon nanofibers by combining electrospinning and controlled Se annealing to construct a flexible self-supporting electrode material. The flexible carbon fiber film obtained by electrospinning exhibits excellent mechanical properties and flexibility; the layered porous carbon fiber electrode after pore formation has a high specific surface area, increasing the active sites of the electrode and improving the sulfur loading; the N and Se co-doped carbon nanofiber framework of the composite electrode can solve the problem of poor electrode electronic conductivity. This invention can prepare a high-performance electrode with good flexibility without the need for current collectors, conductive agents, and binders, meeting the application requirements of flexible electronic devices and wearable electronic devices.

[0017] Further, in step S1, the carbon source includes one or more combinations of polyacrylonitrile, polyvinylpyrrolidone, and polyvinylidene fluoride; the niobium salt includes one or more combinations of niobium chloride, niobium nitrate, niobium sulfate, niobium nitrate acyl, and niobium ammonium sulfate; the pore-forming agent includes polymethyl methacrylate and / or polystyrene microspheres; and the solvent includes N,N-dimethylformamide and / or N-methylpyrrolidone.

[0018] Further, in step S1, the weight of the pore-forming agent accounts for 5% to 20% of the total solid weight in the spinning solution; the weight-to-volume ratio of the carbon source to the solvent is 1:(5 to 10) g / mL; and the mass ratio of the niobium salt to the carbon source is (0.4 to 1):1.

[0019] Further, in step S1, during electrospinning, the voltage is 15-20V, the distance between the needle and the receiving device is 10-20cm, the rotation speed of the roller collecting device is 50-300r / min, and the flow rate of the microfluidic pump is controlled at 0.1-1mL / h.

[0020] Furthermore, in step S2, the temperature of the pre-oxidation treatment is 150–300℃ and the time is 1–5h; the temperature of the pore-forming carbonization treatment is 650–850℃ and the time is 1–5h.

[0021] Further, in step S3, the weight ratio of selenium powder to the second product is (2-8):1; the temperature of the selenization treatment is 550-750℃ and the time is 1-5h. Under high temperature conditions, the selenium powder volatilizes and diffuses onto the carbon nanofibers and undergoes a selenization reaction to obtain a flexible electrode material.

[0022] Further, in step S4, the sulfur loading treatment includes: mixing and melting the flexible electrode material with sulfur powder or dripping a sulfur-containing solution onto the flexible electrode material.

[0023] Preferably, in step S4, the sulfur loading treatment includes the following steps: preparing a drop-coating solution by mixing elemental sulfur and carbon disulfide at a mass-to-volume ratio of 100–400 mg / ml; cutting the flexible electrode material into electrode sheets; repeatedly drop-coating the electrode sheets with the solution onto the electrode sheets; drying the sulfur-loaded electrode sheets; and then heat-treating them at 155–180°C for 2–3 hours to remove excess sulfur, thereby obtaining the lithium-sulfur battery cathode material containing heterostructure materials. Compared with mixed hot-melt methods, the sulfur loading method of drop-coating with a sulfur-containing solution allows for precise control of the sulfur loading amount.

[0024] In this invention, by optimizing and adjusting the key parameters in each preparation step, the electrochemical performance of the electrode material can be further improved, while the cathode material can be made more flexible.

[0025] Preferably, in step S1, the flow rate of the microfluidic pump is controlled at 0.3–0.5 mL / h; in step S2, the pre-oxidation treatment temperature is 150–280℃ for 1–2 h; the pore-forming carbonization treatment temperature is 700–850℃ for 2–3 h, and the heating rate is 2–3℃ / min; in step S4, sulfur loading treatment is performed by drop-coating a sulfur-containing solution, and the heat treatment temperature is 155–165℃ for 2–3 h. The cathode material prepared under the above conditions exhibits better flexibility and superior electrochemical performance.

[0026] The second objective of this invention is to provide a flexible lithium-sulfur battery cathode material containing heterostructure materials, prepared by the preparation method described in the first objective of this invention.

[0027] In this invention, the heterostructure Nb₂O₅-NbSe₂ plays an adsorption and catalytic role in the electrode. Controlling the loading of the heterostructure within a reasonable range ensures better adsorption-catalysis performance. Studies have shown that excessively high loading of the heterostructure Nb₂O₅-NbSe₂ can cause unnecessary side reactions, while insufficient loading will prevent it from functioning effectively. A suitable loading will help improve the cycle stability of the battery.

[0028] Furthermore, in the preparation method of the present invention, the factors affecting the loading of the heterostructure are multifaceted, including: the amount of niobium source added during electrospinning, the temperature and time of the pre-oxidation stage, the temperature and time of the pore-forming carbonization reaction, and the ratio of selenium powder to fiber in the selenization reaction stage. Preferably, in step S1, the mass ratio of niobium salt to carbon source is (0.4-1):1; in step S2, the temperature of the pre-oxidation treatment is 150-280°C, and the time is 1-2 hours; the temperature of the pore-forming carbonization treatment is 700-850°C, and the time is 2-3 hours; in step S3, the weight ratio of selenium powder to the second product is (2-8):1. Under the above conditions, the loading of the heterostructure Nb2O5-NbSe2 in the electrode can be controlled within a more suitable range.

[0029] Preferably, the Nb₂O₅-NbSe₂ heterostructure loading in the lithium-sulfur battery cathode material is 0.3–0.6 mg / cm³. 2 .

[0030] The third objective of this invention is to provide an application of the lithium-sulfur battery cathode material containing heterostructure material as described in the second objective of this invention in flexible electronic devices.

[0031] Furthermore, the present invention also provides a lithium-sulfur battery, comprising a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the positive electrode is made of a lithium-sulfur battery positive electrode material containing a heterostructure material as described in the second objective of the present invention.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) This invention provides a method for preparing a lithium-sulfur battery cathode material with a Nb2O5-NbSe2 heterostructure. The method combines electrospinning and controlled Se-annealing to embed the Nb2O5-NbSe2 heterostructure into N and Se co-doped porous carbon nanofibers, constructing a flexible self-supporting electrode material. The flexible carbon fiber film obtained by electrospinning has good mechanical properties; the layered porous carbon fiber electrode after pore formation has a high specific surface area, increasing the active sites of the electrode and improving the sulfur loading; the N and Se co-doped carbon nanofiber framework of the composite electrode can solve the problem of poor electrode electronic conductivity.

[0034] (2) The lithium-sulfur battery cathode material with Nb2O5-NbSe2 heterostructure obtained by the present invention has the adsorption effect on polysulfides and the catalytic acceleration of polysulfide conversion. Thus, it has the dual effect of "adsorption-catalysis" on polysulfides, which can solve the problems of "shuttle effect" and poor polysulfide reaction kinetics in lithium-sulfur batteries, thereby improving the energy density and cycle stability of lithium-sulfur batteries and providing new ideas for their commercial application.

[0035] (3) The lithium-sulfur battery cathode material with Nb2O5-NbSe2 heterostructure provided by the present invention has a simple and easy preparation method, is easy to adjust and industrialize. The resulting flexible self-supporting lithium-sulfur battery cathode material has good mechanical properties and conductivity. It does not require conductive agents and binders, which is beneficial to improving the sulfur loading and battery energy density. It has broad prospects for promotion and application in the fields of flexible electronic devices and wearable electronic devices. Attached Figure Description

[0036] Figure 1 The images show the physical and SEM images of the Nb2O5-NbSe2 / NSeCNF@S composite cathode material prepared in Example 1 of this invention; (a) a photograph of the composite cathode material in a torsional state; (b) a physical image of the composite cathode material; and (c) an SEM image of the composite cathode material.

[0037] Figure 2 The image shows the XRD pattern of the Nb2O5-NbSe2 heterostructure in the Nb2O5-NbSe2 / NSeCNF@S composite cathode material prepared in Example 1 of this invention.

[0038] Figure 3 The graph shows a comparison of the long-cycle performance of the Nb2O5-NbSe2 / NSeCNF@S cathode prepared in Example 1 of this invention with the CNT@S cathode of Comparative Example 1 and the CNF@S cathode of Comparative Example 2 at a current density of 2C.

[0039] Figure 4 The charge-discharge curves of the Nb2O5-NbSe2 / NSeCNF@S cathode prepared in Example 1 of this invention at a current density of 1C.

[0040] Figure 5 The capacity comparison chart shows the Nb2O5-NbSe2 / NSeCNF@S cathode prepared in Example 1 of this invention, the Nb2O5 / CNFs@S cathode of Comparative Example 3, and the CNF@S cathode of Comparative Example 2 at different rates. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0043] This invention provides a method for preparing a flexible lithium-sulfur battery cathode material containing heterostructure materials, characterized by comprising the following steps:

[0044] Step 1: Dissolve the carbon source, niobium salt, and pore-forming agent in a solvent to obtain a spinning solution, and then electrospin to obtain the first product; wherein, the carbon source includes one or more combinations of polyacrylonitrile, polyvinylpyrrolidone, and polyvinylidene fluoride; the niobium salt includes one or more combinations of niobium chloride, niobium nitrate, niobium sulfate, niobium nitrate, and niobium ammonium sulfate; the pore-forming agent includes polymethyl methacrylate and / or polystyrene microspheres; the solvent includes N,N-dimethylformamide and / or N-methylpyrrolidone; the weight of the pore-forming agent accounts for 5% to 20% of the total solid weight in the spinning solution; the weight-to-volume ratio of carbon source to solvent is 1:(5-10) g / mL; the mass ratio of niobium salt to carbon source is (0.4-1):1; in electrospinning, the voltage is 15-20V, the distance between the needle and the receiving device is 10-20cm, the rotation speed of the roller collecting device is 50-300r / min, and the flow rate of the microfluidic pump is 0.3-0.5mL / h;

[0045] Step 2: The first product is dried, then pre-oxidized, and then placed in an inert atmosphere for pore-forming carbonization to obtain the second product; wherein, the temperature of the pre-oxidation treatment is 150-300℃ and the time is 1-5h; the temperature of the pore-forming carbonization treatment is 650-850℃ and the time is 1-5h, and the heating rate is 2-3℃ / min.

[0046] Step 3: Under a reducing atmosphere, the second product is mixed with selenium powder for selenization treatment to obtain a flexible porous carbon nanofiber self-supporting electrode material with Nb2O5-NbSe2 heterostructure embedded with N and Se co-doped materials; wherein, the weight ratio of selenium powder to the second product is (2-8):1; the selenization treatment temperature is 550-750℃ and the time is 1-5h.

[0047] Step 4: The flexible electrode material obtained in Step 3 is subjected to sulfur loading treatment to obtain a lithium-sulfur battery cathode material containing heterostructure material. The sulfur loading treatment includes: mixing the flexible electrode material with sulfur powder and hot-melting it or dripping a sulfur-containing solution onto the flexible electrode material. When dripping a sulfur-containing solution onto the flexible electrode material, the following steps are included: preparing a dripping solution by mixing elemental sulfur and carbon disulfide at a mass-volume ratio of 100-400 mg / ml; cutting the flexible electrode material into electrode sheets; repeatedly dripping the dripping solution onto the electrode sheets; drying the sulfur-loaded electrode sheets; and then heat-treating them at 155-180℃ for 2-3 hours to remove excess sulfur, thereby obtaining an Nb2O5-NbSe2 heterostructure embedded N, S co-doped porous carbon nanofiber composite sulfur (Nb2O5-NbSe2 / NSeCNF@S) electrode, which is a lithium-sulfur battery cathode material containing heterostructure material.

[0048] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0049] Example 1

[0050] This embodiment provides a lithium-sulfur battery cathode material containing a heterostructure material, and its preparation method includes the following steps:

[0051] Step 1: Dissolve 1.3g PAN and 0.1g PMMA in 6mL DMF in an oil bath at 60℃ and stir for 5 hours. Simultaneously, dissolve 0.5g NbCl5 in 5mL DMF and stir for 2 hours. Then mix the two solutions together and stir for 5 hours to obtain the electrospinning precursor solution. Specific electrospinning parameters are as follows: Place 4mL of the precursor solution in a syringe, select an electrospinning voltage of 18kV, use aluminum foil for collection (15cm from the needle), and set the microfluidic pump flow rate to 0.5mL / h.

[0052] Step 2: Place the spun product in a vacuum drying oven at 60℃ for 12 hours. After drying, remove the spun product from the aluminum foil and place it in a muffle furnace at 240℃ for 1 hour, with a heating rate of 5℃ / min. Then, transfer the pre-oxidized product to a tube furnace and introduce inert argon gas. Heat the product to 850℃ at a heating rate of 5℃ / min and hold for 2 hours.

[0053] Step 3: Mix the product from Step 2 and selenium powder in a weight ratio of 1:5 in a tube furnace, introduce an argon / hydrogen mixture, heat to 650°C at a heating rate of 5°C / min, and hold for 1.5 hours to obtain the composite material.

[0054] Step 4: Sulfur is loaded using a drop-coating method. 0.2g of sulfur powder is dissolved in 2mL of carbon disulfide to prepare drop-coating solution A, which is then stored at low temperature. The composite material obtained in step 3 is cut into φ10mm electrode sheets using a cutting machine. 10µL of drop-coating solution A is slowly drop-coated onto the electrode sheet. After drying, the process is repeated 5 times. The product after drop-coating is transferred to an oven and dried for 30min. Subsequently, the electrode sheet is placed in a ceramic boat and heat-treated at 160℃ for 3 hours to remove excess sulfur from the electrode surface, thus obtaining a lithium-sulfur battery Nb2O5-NbSe2 / NSeCNF@S cathode material. In the above lithium-sulfur battery cathode material, the Nb2O5-NbSe2 heterostructure loading is 0.5mg / cm³. 2 .

[0055] Example 2

[0056] This embodiment provides a lithium-sulfur battery cathode material containing a heterostructure material, and its preparation method includes the following steps:

[0057] Step 1: Dissolve 1g of PAN and 0.2g of PMMA in 5mL of DMF in an oil bath at 60℃ for 5 hours. Simultaneously, dissolve 0.5g of NbCl5 in 5mL of DMF and stir for 2 hours. Then mix the two solutions together and stir for 5 hours to obtain the electrospinning precursor solution. Specific electrospinning parameters are as follows: Place 4mL of the precursor solution in a syringe, select an electrospinning voltage of 18kV, use aluminum foil for collection (18cm from the needle), and set the microfluidic pump flow rate to 0.3mL / h.

[0058] Step 2: Place the spun product in a vacuum drying oven at 60℃ for 12 hours. After drying, remove the spun product from the aluminum foil and place it in a muffle furnace at 150℃ for 3 hours for pre-oxidation, with a heating rate of 5℃ / min. Then, transfer the pre-oxidized product to a tube furnace and introduce inert argon gas. Heat the product to 700℃ at a heating rate of 3℃ / min and hold for 3 hours.

[0059] Step 3: Mix the product from Step 2 with selenium powder at a weight ratio of 1:2 in a tube furnace, introduce an argon / hydrogen mixture, heat to 550°C at a heating rate of 5°C / min, and hold for 4 hours to obtain the composite material.

[0060] Step 4: Sulfur is loaded using a drop-coating method. 0.3g of sulfur powder is dissolved in 2mL of carbon disulfide. Simultaneously, the composite material obtained in Step B is cut into electrode sheets using a cutting machine. The aforementioned carbon disulfide solution is drop-coated onto the composite electrode sheet, dried in a drying oven, and then placed in a ceramic boat and kept at a high temperature of 155℃ for 3 hours to remove excess sulfur from the electrode surface, thus obtaining a lithium-sulfur battery Nb2O5-NbSe2 / NSeCNF@S cathode material. In the above lithium-sulfur battery cathode material, the Nb2O5-NbSe2 heterostructure loading is 0.35mg / cm³. 2 .

[0061] Example 3

[0062] This embodiment provides a lithium-sulfur battery cathode material containing a heterostructure material, and its preparation method includes the following steps:

[0063] Step 1: Dissolve 1g of PAN and 0.1g of PMMA in 5mL of DMF in an oil bath at 60℃ for 5 hours. Simultaneously, dissolve 0.5g of NbCl5 in 5mL of DMF and stir for 5 hours. Then mix the two solutions together and stir for 5 hours to obtain the electrospinning precursor solution. Specific electrospinning parameters are as follows: Place 4mL of the precursor solution in a syringe, select an electrospinning voltage of 18kV, use aluminum foil for collection (15cm from the needle), and set the microfluidic pump flow rate to 0.4mL / h.

[0064] Step 2: Place the spun product in a vacuum drying oven and dry at 60℃ for 12 hours. After drying, remove the spun product from the aluminum foil and place it in a muffle furnace for pre-oxidation at 280℃ for 2 hours, with a heating rate of 2℃ / min. Then, transfer the pre-oxidized product to a tube furnace and introduce inert argon gas. Heat the product to 750℃ at a heating rate of 3℃ / min and hold for 2 hours.

[0065] Step 3: Mix the product from Step 2 and selenium powder in a weight ratio of 1:8 in a tube furnace, introduce an argon / hydrogen mixture, heat to 750°C at a heating rate of 2°C / min, and hold for 1 hour to obtain the composite material.

[0066] Step 4: Sulfur is loaded using a drop-coating method. 0.4g of sulfur powder is dissolved in 2mL of carbon disulfide. Simultaneously, the composite material obtained in Step B is cut into electrode sheets using a cutting machine. The aforementioned carbon disulfide solution is drop-coated onto the composite electrode sheet, dried in a drying oven, and then placed in a ceramic boat and kept at 180℃ for 2 hours to remove excess sulfur from the electrode surface, thus obtaining a lithium-sulfur battery Nb2O5-NbSe2 / NSeCNF@S cathode material. In the above lithium-sulfur battery cathode material, the Nb2O5-NbSe2 heterostructure loading is 0.6mg / cm³. 2 .

[0067] Comparative Example 1

[0068] This comparative example provides a carbon nanotube and sulfur composite cathode material CNT@S.

[0069] Comparative Example 2

[0070] This comparative example provides a carbon nanofiber composite sulfur cathode material CNFs@S, the preparation method of which includes the following steps:

[0071] Step 1: Dissolve 1.3g PAN and 0.1g PMMA in 6mL DMF in an oil bath and stir for 5 hours at 60℃ to prepare the electrospinning precursor solution. Specific electrospinning parameters are selected as follows: Take 4mL of the precursor solution in a syringe, select an electrospinning voltage of 18kV, use aluminum foil for collection, with the collector 15cm from the needle tip, and set the microfluidic pump flow rate to 0.5mL / h.

[0072] Step 2: Place the spun product in a vacuum drying oven at 60℃ for 12 hours. After drying, remove the spun product from the aluminum foil and place it in a muffle furnace at 240℃ for 1 hour, with a heating rate of 5℃ / min. Then, transfer the pre-oxidized product to a tube furnace and introduce inert argon gas. Heat the product to 850℃ at a heating rate of 5℃ / min and hold for 2 hours.

[0073] Step 3: Sulfur is loaded using a drop-coating method. 0.2g of sulfur powder is dissolved in 2mL of carbon disulfide to prepare drop-coating solution A, which is then stored at low temperature. The material obtained in step 2 is cut into φ10mm electrode sheets using a cutting machine. 10µL of drop-coating solution A is slowly drop-coated onto the electrode sheet. After drying, the process is repeated 5 times. The product after drop-coating is transferred to an oven and dried for 30min. Subsequently, the electrode sheet is placed in a ceramic boat and heat-treated at 160℃ for 3 hours to remove excess sulfur from the electrode surface, thus obtaining the carbon nanofiber composite sulfur cathode material CNFs@S.

[0074] Comparative Example 3

[0075] This comparative example provides a niobium pentoxide in-situ embedded carbon nanofiber composite sulfur cathode Nb2O5 / CNFs@S, the preparation method of which includes the following steps:

[0076] Step 1: Dissolve 1.3g PAN and 0.1g PMMA in 6mL DMF in an oil bath at 60℃ and stir for 5 hours. Simultaneously, dissolve 0.5g NbCl5 in 5mL DMF and stir for 2 hours. Then mix the two solutions together and stir for 5 hours to obtain the electrospinning precursor solution. Specific electrospinning parameters are as follows: Place 4mL of the precursor solution in a syringe, select an electrospinning voltage of 18kV, use aluminum foil for collection (15cm from the needle), and set the microfluidic pump flow rate to 0.5mL / h.

[0077] Step 2: Place the spun product in a vacuum drying oven at 60℃ for 12 hours. After drying, remove the spun product from the aluminum foil and place it in a muffle furnace at 240℃ for 1 hour, with a heating rate of 5℃ / min. Then, transfer the pre-oxidized product to a tube furnace and introduce inert argon gas. Heat the product to 850℃ at a heating rate of 5℃ / min and hold for 2 hours.

[0078] Step 3: Sulfur is loaded using a drop-coating method. 0.2g of sulfur powder is dissolved in 2mL of carbon disulfide to prepare drop-coating solution A, which is then stored at low temperature. The composite material obtained in Step 3 is cut into φ10mm electrode sheets using a cutting machine. 10µL of drop-coating solution A is slowly drop-coated onto the electrode sheet and allowed to dry. This process is repeated 5 times. The drop-coated product is then transferred to an oven and dried for 30min. Subsequently, the electrode sheet is placed in a ceramic boat and heat-treated at 160℃ for 3 hours to remove excess sulfur from the electrode surface, thus obtaining a niobium pentoxide in-situ embedded carbon nanofiber composite sulfur cathode Nb2O5 / CNFs@S.

[0079] Characterization and performance testing

[0080] according to Figure 1As can be seen from the physical image of the Nb2O5-NbSe2 / NSeCNF@S composite cathode material provided, the composite cathode material prepared by this invention has good flexibility and can be freely twisted, which can meet the application requirements of flexible electronic devices and wearable electronic devices for flexible electrode materials.

[0081] The Nb2O5-NbSe2 / NSeCNF@S cathode prepared in Example 1 and the electrodes prepared in Comparative Examples 1-3 were subjected to application performance tests. The test conditions and results are as follows. Figure 3-5 As shown.

[0082] according to Figure 3 The comparison chart of the long-term cycling performance of the Nb2O5-NbSe2 / NSeCNF@S cathode prepared in Example 1 with the CNT@S cathode prepared in Comparative Example 1 and the CNF@S cathode prepared in Comparative Example 2 at a current density of 2C shows that the Nb2O5-NbSe2 / NSeCNF@S cathode prepared in this invention has good cycling stability, maintaining a capacity of over 600 mAh / g after 470+ cycles, with a capacity retention rate as high as 85%.

[0083] according to Figure 4 Charge-discharge curves of the Nb₂O₅-NbSe₂ / NSeCNF@S cathode prepared in Example 1 at 1C current density (sulfur loading 3.4 mg / cm³). 2 ), Figure 5 The capacity comparison charts of Nb2O5-NbSe2 / NSeCNF@S cathode, Nb2O5 / CNFs@S prepared in Comparative Example 3, and CNF@S prepared in Comparative Example 2 at different rates show that Nb2O5-NbSe2 / NSeCNF@S exhibits significantly superior rate performance. This indicates that the flexible lithium-sulfur battery cathode material containing heterostructure materials provided by this invention can effectively solve the problems of "shuttle effect" and poor reaction kinetics faced by lithium-sulfur batteries, thereby improving the electrochemical performance and cycle stability of lithium-sulfur batteries.

[0084] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a flexible lithium-sulfur battery cathode material containing a heterostructure material, characterized in that, Includes the following steps: S1. Dissolve carbon source, niobium salt and pore-forming agent in solvent to obtain spinning solution, and obtain the first product by electrospinning; S2. The first product is dried, then pre-oxidized, and then placed in an inert atmosphere for pore-forming carbonization to obtain the second product; the temperature of the pre-oxidation treatment is 150~300℃ and the time is 1~5h; the temperature of the pore-forming carbonization treatment is 650~850℃ and the time is 1~5h. S3. Under a reducing atmosphere, the second product is mixed with selenium powder and subjected to selenization treatment to obtain a flexible electrode material; the weight ratio of the selenium powder to the second product is (2~8):1; the selenization treatment temperature is 550~750℃ and the time is 1~5h. S4. The flexible electrode material is subjected to sulfur loading treatment to obtain a lithium-sulfur battery cathode material containing heterostructure material.

2. The preparation method according to claim 1, characterized in that, In step S1, the carbon source includes one or more combinations of polyacrylonitrile, polyvinylpyrrolidone, and polyvinylidene fluoride; the niobium salt includes one or more combinations of niobium chloride, niobium nitrate, niobium sulfate, niobium nitrate acyl, and niobium ammonium sulfate; the pore-forming agent includes polymethyl methacrylate and / or polystyrene microspheres; and the solvent includes N,N-dimethylformamide and / or N-methylpyrrolidone.

3. The preparation method according to claim 1, characterized in that, In step S1, the weight of the pore-forming agent accounts for 5% to 20% of the total solid weight in the spinning solution; the weight-to-volume ratio of carbon source to solvent is 1:(5~10) g / mL; and the mass ratio of niobium salt to carbon source is (0.4~1):

1.

4. The preparation method according to claim 1, characterized in that, In step S1, during electrospinning, the voltage is 15~20V, the distance between the needle and the receiving device is 10~20cm, the rotation speed of the roller collecting device is 50~300 r / min, and the flow rate of the microfluidic pump is 0.1~1mL / h.

5. The preparation method according to claim 1, characterized in that, In step S4, the sulfur loading treatment includes: mixing and melting the flexible electrode material with sulfur powder or dripping a sulfur-containing solution onto the flexible electrode material.

6. The preparation method according to claim 5, characterized in that, In step S4, the sulfur loading treatment includes the following steps: preparing a drop coating solution by mixing elemental sulfur and carbon disulfide at a mass-volume ratio of 100~400 mg / mL; cutting the flexible electrode material into electrode sheets; applying the drop coating solution onto the electrode sheets multiple times; drying the sulfur-loaded electrode sheets; and then heat-treating them at 155~180℃ for 2~3 hours to remove excess sulfur, thereby obtaining the lithium-sulfur battery cathode material containing heterostructure materials.

7. A lithium-sulfur battery cathode material containing a heterostructure material prepared by the preparation method according to any one of claims 1-6, characterized in that, In the lithium-sulfur battery cathode material, the loading of the Nb₂O₅-NbSe₂ heterostructure is 0.3~0.6 mg / cm³. 2 .

8. The application of a lithium-sulfur battery cathode material containing a heterostructure material according to claim 7 in flexible electronic devices.

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