Metal-doped nitride heterojunction catalyst, preparation method and application of metal-doped nitride heterojunction catalyst in lithium / sodium-sulfur battery

Abstract

The invention discloses a metal-doped nitride heterojunction catalyst, a preparation method thereof and application of a lithium / sodium-sulfur battery, and belongs to the field of alkali metal sulfur-based battery electrocatalyst materials. The preparation method comprises the following steps: (1) dissolving cobalt nitrate, ammonium molybdate, ammonium chloride and urea in deionized water according to a molar mass ratio of 12.8: 1.6: 8: 8; (2) heating in an oil bath at 100 DEG C for 2 hours in an argon atmosphere to obtain a purple clear solution; and (3) centrifugally washing the precipitate with deionized water for three times, freeze-drying to obtain a purple floccule, and calcining the purple floccule in a mixed atmosphere of ammonia gas and argon gas in a ratio of 1: 4 at 700 DEG C for 3 hours to obtain the metal-doped nitride heterojunction catalyst. The method is low in production cost and simple in manufacturing process, and the catalytic material has the advantages of high energy density, long cycle life and the like when applied to lithium / sodium-sulfur batteries.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalyst materials for alkali metal sulfur-based batteries, and particularly relates to a metal-doped transition metal nitride heterogeneous catalyst for lithium / sodium sulfur batteries and a preparation method thereof. Background Art

[0002] The continuous consumption of non-renewable energy sources such as coal and oil has posed a serious threat to the sustainable development of the global ecosystem and human society. From air pollution to water pollution and then to soil pollution, it not only threatens the survival of organisms on Earth but also brings huge challenges to human health and the stable development of the economy.

[0003] In this context, as one of the key enabling technologies in the new energy field, the research and development of the cathode materials of lithium-ion batteries play a crucial role in promoting energy transformation and achieving green and sustainable development. An ideal cathode material for lithium-ion batteries should have a high redox potential to increase the output voltage and energy density of the battery; a high packing density to store more electrical energy in a limited space; good stability to ensure stable battery performance during long-term charge and discharge cycles and extend the service life; high electrical conductivity to accelerate the charge transfer rate and improve the charge and discharge efficiency of the battery; at the same time, low production cost and simple manufacturing process, which are conducive to large-scale industrial applications. These characteristics are of epoch-making significance for solving the current increasingly severe energy, environmental and other problems, and are expected to provide strong support for global energy structure optimization and environmental protection.

[0004] In recent years, lithium / sodium sulfur batteries, as a highly promising next-generation new lithium battery technology, have attracted much attention due to their unique electrochemical properties. As a conversion-type material, its cathode material has a theoretical capacity of up to 1675 mAh / g, far exceeding that of traditional lithium-ion battery cathode materials, providing broad space for the research and development of high-energy-density energy storage devices. Its main advantages are reflected in three aspects: one is the high theoretical energy density, which can store a large amount of electrical energy on the basis of light weight, meeting the requirements of long-range electric vehicles and portable electronic devices; the second is relatively low cost, with rich sulfur resources and low prices, reducing the production cost of the battery and being conducive to large-scale promotion; the third is relatively environmentally friendly, with less negative impact on the environment during production, use and recycling, conforming to the concept of sustainable development.

[0005] However, during the process of lithium / sodium-sulfur batteries moving from the laboratory to commercial applications, there are still many problems that need to be solved urgently. The volume expansion problem can lead to the destruction of the battery structure and affect the cycling performance; the slow reaction kinetics result in low efficiency of the battery during high-rate charge and discharge, unable to meet the requirements of rapid charge and discharge; the relatively short cycle life limits its economy and reliability in practical use; the poor conductivity further restricts the power output of the battery; and the "shuttle effect" caused by the dissolution of polysulfides not only reduces the Coulomb efficiency of the battery, but also causes corrosion and passivation of the positive and negative electrodes, seriously hindering the commercialization process of lithium-sulfur batteries and becoming the key bottleneck restricting their large-scale application.

[0006] In response to these challenges, the application of electrocatalysts has brought new hope for the improvement of the performance of lithium / sodium-sulfur batteries. Electrocatalysts can effectively accelerate the redox reaction kinetics process of lithium / sodium-sulfur batteries, significantly reduce the reaction activation energy, thereby accelerating the charge and discharge rate and improving the rate performance of the battery. At the same time, by reasonably designing and selecting electrocatalysts, polysulfides can be effectively adsorbed and transformed, inhibiting their dissolution and shuttle in the electrolyte, and fundamentally solving a series of problems brought by the "shuttle effect". This can not only significantly improve the electrochemical performance of lithium / sodium-sulfur batteries, including enhancing capacity, extending cycle life, and increasing stability, but also provide solid technical support for their commercial application, promote the innovation and development of new energy battery technologies, and contribute to the realization of global energy transformation and sustainable development goals.

[0007] Publication number CN115966660A discloses a preparation method of a nickel phthalocyanine / super-large specific surface area porous carbon composite material. Phthalic anhydride, urea, ammonium chloride, nickel chloride hexahydrate and ammonium molybdate tetrahydrate are ground evenly and then calcined to prepare a crude product of nickel phthalocyanine. Then, the washed nickel phthalocyanine and the super-large specific surface area porous carbon material are dissolved and mixed to obtain the composite material. This composite material is used as the carrier of the positive electrode active material of the lithium-sulfur battery. The performance of this composite material needs to be further improved. Summary of the Invention

[0008] The present invention aims to solve the above problems of the prior art. A preparation method of a metal-doped nitride heterojunction catalyst and its application in lithium / sodium-sulfur batteries are proposed.

[0009] The technical solution adopted by the present invention is: a preparation method of a metal-doped nitride heterojunction catalyst, including the following steps:

[0010] Dissolve cobalt nitrate, ammonium molybdate, ammonium chloride, and urea with a molar mass ratio of 12.8:1.6:8:8 in deionized water;

[0011] Under the atmosphere of argon, heat in an oil bath at 100 °C for 2 hours to obtain a purple clear solution;

[0012] The precipitate was washed three times by centrifugation with deionized water and then freeze-dried to obtain a purple flocculent, which was then calcined at 700° C. for 3 hours in a mixed atmosphere of ammonia:argon=1:4 to obtain a metal-doped nitride heterojunction catalyst.

[0013] Further, the method of dissolving cobalt nitrate, ammonium molybdate, ammonium chloride and urea in a molar mass ratio of 12.8:1.6:8:8 in deionized water specifically includes: taking 3.725g of cobalt nitrate, 1.977g of ammonium molybdate, 0.427g of ammonium chloride and 0.48g of urea into a three-necked flask, and adding 200mL of deionized water to dissolve.

[0014] Furthermore, the 100° C. oil bath was heated for 2 hours, and the timing began when the temperature reached 100° C.

[0015] Furthermore, the heating rate of the calcination at 700° C. for 3 hours in the mixed atmosphere of ammonia:argon=1:4 is 2.5° C. / min.

[0016] According to the above preparation method, the present invention provides a metal-doped nitride heterojunction catalyst prepared by the above method.

[0017] The present invention also provides the use of the metal-doped nitride heterojunction catalyst in preparing a lithium / sodium-sulfur battery. Specifically, the metal-doped nitride heterojunction catalyst is used to prepare a positive electrode material of a battery.

[0018] The present invention provides a lithium / sodium-sulfur battery positive electrode material, which is prepared by mixing the metal-doped nitride heterojunction catalyst with sulfur and heating the mixture in an argon atmosphere at 155° C., wherein the mass ratio of the metal-doped nitride heterojunction catalyst to sulfur is 2:8 or 3:7.

[0019] The present invention provides a lithium-sulfur battery, which is prepared by the following method:

[0020] Preparation of positive electrode material: The metal-doped nitride heterojunction catalyst according to claim 5 and elemental sulfur are placed in an agate mortar at a mass ratio of 2:8, and the mixture is fully ground and mixed, and a constant temperature heat treatment is performed at 155° C. for 12 hours under an argon protective atmosphere to obtain a sulfur positive electrode composite material;

[0021] Preparation of electrode slurry: The sulfur cathode composite material is mixed with conductive carbon black and polyvinylidene fluoride binder in a mass ratio of 8:1:1, N-methylpyrrolidone solvent is added, and the mixture is continuously stirred for 12 hours by a planetary mixer to obtain a uniformly dispersed electrode slurry;

[0022] Pole forming and drying: The slurry is evenly coated on the surface of the aluminum foil current collector by a doctor blade coating method, and then the coated pole is placed in a 60°C vacuum drying oven for 12 hours to ensure that the solvent is completely evaporated;

[0023] Post-treatment of the electrode sheet: Use a precision punching machine to process the dried electrode sheet into a circular electrode sheet;

[0024] Battery assembly: In an argon glove box, perform according to the standard CR2032 button cell assembly process: sequentially load the positive electrode case, sulfur positive electrode sheet, 50 μL of lithium-sulfur special electrolyte, Celgard 2400 polypropylene separator, lithium metal negative electrode sheet, stainless steel gasket and negative electrode case, and seal and form it by a hydraulic sealing machine.

[0025] The present invention provides a sodium-sulfur battery, which is prepared by the following method:

[0026] Preparation of sulfur-based composite material: Adopt the mechanochemical-melting perfusion method, place the metal-doped nitride heterojunction catalyst described in claim 5 and sublimed sulfur in a mass ratio of 3:7 in an agate mortar and grind for 30 minutes, and heat up to 155 °C at a rate of 2 °C / min under an argon protection atmosphere for 12 hours of constant temperature thermal diffusion treatment to obtain a sulfur-catalyst composite positive electrode material;

[0027] Preparation of electrode slurry: Add the sulfur-catalyst composite positive electrode material, Super P conductive carbon black and polyvinylidene fluoride binder to a planetary mixer according to a mass ratio of 8:1:1, add N-methylpyrrolidone solvent to adjust the viscosity of the slurry, and continuously stir for 12 hours by the planetary mixer to obtain a uniformly dispersed electrode slurry;

[0028] Electrode sheet drying process: Use the doctor blade coating method to uniformly coat the slurry on the surface of the aluminum foil current collector, and then transfer it to a programmable temperature vacuum drying oven, and perform stepwise drying at 60 °C and a vacuum degree of -0.1 MPa: first rise to 40 °C at a rate of 5 °C / min and maintain for 2 hours to remove the surface solvent, then rise to 60 °C and keep for 10 hours to ensure the volatilization of the deep solvent, and finally control the water content of the electrode sheet below 50 ppm;

[0029] Forming and quantification of the electrode sheet: Use a precision punching machine to process the electrode sheet into a standard round sheet;

[0030] Battery encapsulation: Assemble a CR2032 type button cell in an argon glove box: sequentially place the positive electrode case, sulfur positive electrode sheet, 120 μL of sodium-sulfur electrolyte, Whatman GF / D glass fiber separator, sodium metal negative electrode, spring gasket and negative electrode case, and seal and form it by a hydraulic sealing machine.

[0031] The advantages and beneficial effects of the present invention are as follows:

[0032] The present invention relates to a metal-doped nitride heterojunction catalyst for lithium / sodium-sulfur batteries and a preparation method thereof. The process route combining a chemical solution method and a high-temperature calcination method is innovatively adopted to successfully prepare a metal-doped nitride heterojunction catalyst with excellent performance. When the catalyst is applied to the positive electrode material of lithium / sodium-sulfur batteries, it exhibits excellent high-rate performance and long-life cycle performance, and can significantly improve the reaction kinetics of lithium / sodium-sulfur batteries during the charging and discharging process, thereby accelerating the charging and discharging speed, improving the battery efficiency and extending its service life.

[0033] More importantly, the lithium / sodium-sulfur battery catalyst material of the present invention has many outstanding advantages while having excellent performance. Its production cost is low, the manufacturing process is simple and easy, and the entire preparation process is green and pollution-free, which fully meets the current environmental protection concept and the requirements of sustainable development. In summary, the lithium / sodium-sulfur battery catalyst material of the present invention has not only made a major breakthrough in technology, but also has very important practical significance in terms of economic and environmental benefits, showing broad market prospects and huge industrialization potential, and is expected to set off a new technological revolution in the field of new energy, and make positive contributions to promoting the development of green energy.

[0034] In lithium / sodium-sulfur batteries, the multiphase reaction of sulfur and the intermediate products in the electrochemical process may lead to a decrease in battery performance, so introducing a catalyst to promote the reaction of sulfur is a common strategy. The present invention improves the conductivity of the sulfur positive electrode by synthesizing transition metal nitrides, thereby improving its catalytic activity, which helps to improve the performance of lithium / sodium-sulfur batteries. The introduction of metal elements can form a heterogeneous structure, thereby regulating the electronic structure and chemical properties of transition metal nitrides, and playing a synergistic role in adsorption and catalysis of polysulfides. In addition, metal elements can introduce new active sites, which help catalyze the reaction of sulfur and further improve the cycle stability and electrochemical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a process flow chart of the present invention;

[0036] Figure 2 2a is the corresponding TEM image, 2b is the corresponding SAED image, 2c is the corresponding XRD image, and 2d is the corresponding SEM image;

[0037] Figure 3 a is the charge and discharge curves under different rate conditions, 3b is the cycle performance of the lithium-sulfur battery at a rate of 0.1C, 3c is the cyclic voltammetry curve of the lithium-sulfur battery using the catalytic material at different scan rates in an embodiment of the present invention, and 3d is the Li2S nucleation test;

[0038] Figure 4 a is 0.1mv s -1 4b is the cyclic voltammetry curve of the scan rate, and 4b is the charge and discharge curve of the sodium-sulfur battery using the catalyst material in the embodiment of the present invention under 0.1C rate conditions. DETAILED DESCRIPTION

[0039] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

[0040] A method for preparing a metal-doped nitride heterojunction catalyst, as shown in FIG. Figure 1 As shown, the following steps are included:

[0041] Cobalt nitrate, ammonium molybdate, ammonium chloride and urea in a molar mass ratio of 12.8:1.6:8:8 were dissolved in deionized water; heated in an oil bath at 100°C for 2 hours under an argon atmosphere to obtain a purple clear solution; the precipitate was centrifugally washed three times with deionized water and then freeze-dried to obtain a purple flocculent, which was then calcined at 700°C for 3 hours in a mixed atmosphere of ammonia:argon = 1:4 to obtain a metal-doped nitride heterojunction catalyst.

[0042] The metal-doped nitride heterojunction catalyst prepared in the above embodiment can be used in the field of lithium / sodium-sulfur batteries, especially for the problems of slow reaction kinetics and poor cycle stability of sulfur electrode in lithium / sodium-sulfur batteries.

[0043] The synthesis process of the lithium / sodium-sulfur battery catalyst material in the above embodiment specifically includes the following steps: 3.725g of cobalt nitrate, 1.977g of ammonium molybdate, 0.427g of ammonium chloride, and 0.48g of urea are placed in a three-necked flask, and 200mL of deionized water is added to dissolve. Under the protection of argon, the temperature is raised to 100°C and the reaction is carried out for 2h. After cooling, the precipitate is centrifuged and washed three times with deionized water and then freeze-dried to obtain a purple flocculent, which is calcined at 700°C for 3 hours in a mixed atmosphere of ammonia: argon = 1:4 at a heating rate of 2.5°C / min. That is, a metal-doped nitride heterojunction catalyst is obtained. The positive electrode, negative electrode, electrolyte and diaphragm of the present invention are prepared according to the methods commonly used by those skilled in the art (so they are not described here).

[0044] The metal-doped nitride heterojunction catalyst in the above embodiment is used to prepare a lithium-sulfur battery, and the specific steps are as follows: 1) Preparation of composite catalyst: The pre-synthesized metal-doped nitride heterojunction catalyst and elemental sulfur are placed in an agate mortar at a mass ratio of 2:8 and fully ground and mixed. The mixture is transferred to a high-pressure reactor and subjected to a constant temperature heat treatment at 155°C for 12 hours under an argon protective atmosphere to obtain a sulfur-based composite material.

[0045] (2) Preparation of electrode slurry: The obtained sulfur-based composite material is mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent is added and continuously stirred for 12 hours by a planetary mixer to obtain a uniformly dispersed electrode slurry.

[0046] (3) Forming and drying of electrode sheet: The slurry is uniformly coated on the surface of the aluminum foil current collector by the doctor blade coating method, and then the coated electrode sheet is placed in a vacuum drying oven at 60 °C for 12 hours to ensure complete volatilization of the solvent.

[0047] (4) Post-treatment of electrode sheet: The dried electrode sheet is processed into a circular electrode sheet with a diameter of 12 mm using a precision punching machine, and the mass of the electrode sheet is accurately weighed using a microbalance to record the effective active material loading.

[0048] (5) Battery assembly: In an argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the standard CR2032 coin cell assembly process is carried out: the positive electrode case, sulfur positive electrode sheet (sulfur loading of 1.2 mg / cm2), 50 μL of lithium-sulfur special electrolyte (1 M LiTFSI in DOL / DME = 1:1 v / v with 2 wt% LiNO3 additive), Celgard 2400 polypropylene separator, lithium metal negative electrode sheet, stainless steel gasket and negative electrode case are sequentially loaded and sealed and formed by a hydraulic sealing machine.

[0049] A method for preparing a sodium-sulfur battery using a metal-doped nitride heterojunction catalyst, comprising the following steps:

[0050] (1) Preparation of sulfur-based composite material

[0051] Using the mechanochemical-melt perfusion method, the metal-doped nitride heterojunction catalyst and sublimed sulfur are placed in an agate mortar in a mass ratio of 3:7 and ground for 30 minutes to achieve molecular-level mixing. The homogeneous mixture is sealed in a stainless steel high-pressure reactor and heated to 155 °C at a rate of 2 °C / min under an argon protection atmosphere for 12 hours of constant temperature thermal diffusion treatment to obtain a sulfur-catalyst composite positive electrode material.

[0052] (2) Preparation of electrode slurry

[0053] The sulfur composite, Super P conductive carbon black and polyvinylidene fluoride (PVDF) binder are added to a planetary mixer in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) solvent is added to adjust the viscosity of the slurry, and it is continuously stirred for 12 hours by a planetary mixer to obtain a uniformly dispersed electrode slurry.

[0054] (3) Electrode sheet drying process

[0055] Transfer the wet electrode to a programmable temperature-controlled vacuum drying oven and perform stepwise drying at 60 °C and a vacuum degree of -0.1 MPa: first raise the temperature to 40 °C at a rate of 5 °C / min and maintain it for 2 hours to remove the surface solvent, then raise the temperature to 60 °C and hold for 10 hours to ensure the volatilization of the deep-layer solvent. Finally, control the water content of the electrode below 50 ppm.

[0056] (4) Electrode forming and quantification

[0057] Use a precision punching machine (die diameter 12.00 ± 0.05 mm) to process the electrode into standard circular wafers, and use a microbalance (accuracy 0.01 mg) to weigh and record the mass of each wafer. Calculate the active material loading by the difference method, and control the sulfur surface density to be 1.0 ± 0.1 mg / cm 2 (correcting the mass of the aluminum foil substrate).

[0058] (5) Battery encapsulation process

[0059] Assemble a CR2032 coin cell in an argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm): sequentially place the positive electrode case, sulfur positive electrode, 120 μL sodium-sulfur electrolyte (1 M NaClO4 in TEGDME with 0.2 M NaNO3), Whatman GF / D glass fiber separator, sodium metal negative electrode (thickness 200 μm), spring gasket and negative electrode case, and use a hydraulic sealer to seal and form at a pressure of 8 tons.

[0060] Electrochemical analysis of the metal-doped nitride heterojunction catalyst:

[0061] From Figure 2 a shows that MoN indeed corresponds to two phases and has an obvious heterojunction interface. MoN has good conductivity and specific surface area. The introduction of Co provides a large number of active sites, which can effectively accelerate the conversion of polysulfides and effectively inhibit the "shuttle effect" of lithium-sulfur batteries. Figure 2 b respectively proves the coexistence of the (111), (220) lattice planes of Co and the (001), (100), (111), (220) lattice planes of MoN, Figure 2 c shows that there are two phases of MoN in the metal-doped nitride heterojunction catalyst material, namely cubic crystal and hexagonal, Figure 2 d shows that the morphology of the metal-doped nitride heterojunction catalyst material is a rod-like structure, and the elemental mapping of Co / MoN reveals the uniform elemental distribution of the composite material.

[0062] After electrochemical performance testing, Figure 3 a is the charge-discharge curves under the conditions of 0.1C, 0.2C, 0.5C, and 1C. It can be seen that at a high rate of 1C, the battery discharge capacity is 850 mAh / g.

[0063] Figure 3 The long cycle curve of b at 0.1C rate, the initial discharge capacity is 1402.2 mAh·g -1 , after 1000 cycles, the capacity still remains at 1153 mAh·g -1 , and the attenuation rate per cycle is only 0.0017%.

[0064] Figure 3 c are cyclic voltammograms at different scan rates, all showing strong redox peaks.

[0065] Figure 3 d is the Li2S nucleation test, and the deposition capacity in the case of Co-MoN / S is 419.94 mAh g -1 , and its catalysis performance for polysulfides is excellent.

[0066] Figure 4 a is the cyclic voltammogram at a scan rate of 0.1 mV s -1 , all showing strong redox peaks; Figure 4 b is the charge-discharge curve of the sodium-sulfur battery at 0.1C rate.

[0067] Through electrochemical performance tests, the sulfur electrode loaded with the metal-doped nitride heterojunction catalyst can significantly improve the conductivity of the sulfur electrode, effectively inhibit the "shuttle effect" of lithium / sodium-sulfur batteries, show good cycle stability, and exhibit excellent rate performance.

[0068] It should be further clarified that, in the context of the present invention, the terms "comprising", "including" and their derivative terms are given a non-exclusive connotation, aiming to refer to an inclusive listing. This means that a process, method, product or device described as including a series of elements not only includes the listed elements, but may also cover other elements that are not explicitly mentioned but are essentially related to the process, method, product or device. In addition, unless otherwise clearly restricted, the elements defined by "including one..." do not exclude the possibility of the existence of other identical elements on the basis of including this element.

[0069] The embodiments listed in the present invention are only for the interpretation and supplement of the invention content, aiming to provide a more intuitive and comprehensive understanding for technicians, rather than a limitation of the protection scope of the present invention. Based on the content recorded in the present invention, technicians can make reasonable improvements and modifications to the present invention without violating the core of the invention. It should be clear that these equivalent changes and modifications should be included within the protection scope of the present invention.

Claims

1. Metal-doped nitride heterojunction catalyst and preparation method thereof, characterized in that, The following steps are involved: Dissolve cobalt nitrate, ammonium molybdate, ammonium chloride, and urea in a molar mass ratio of 12.8:1.6:8:8 in deionized water; Under an argon atmosphere, heat in an oil bath at 100 °C for 2 h to obtain a purple clear solution; The precipitate was washed three times by centrifugation with deionized water and then freeze-dried to obtain a purple flocculent, which was then calcined at 700° C. for 3 hours in a mixed atmosphere of ammonia:argon=1:4 to obtain a metal-doped nitride heterojunction catalyst.

2. The metal-doped nitride heterojunction catalyst and preparation method according to claim 1, characterized in that: The method of dissolving cobalt nitrate, ammonium molybdate, ammonium chloride and urea in a molar mass ratio of 12.8:1.6:8:8 in deionized water specifically comprises: placing 3.725 g of cobalt nitrate, 1.977 g of ammonium molybdate, 0.427 g of ammonium chloride and 0.48 g of urea in a three-necked flask, and adding 200 mL of deionized water to dissolve the mixture.

3. The metal-doped nitride heterojunction catalyst and preparation method according to claim 1, wherein: The 100°C oil bath was heated for 2 hours, and the timing began when the temperature reached 100°C.

4. The metal-doped nitride heterojunction catalyst and preparation method according to claim 1, wherein: The heating rate of the calcination at 700° C. for 3 hours in a mixed atmosphere of ammonia:argon=1:4 is 2.5° C. / min.

5. Metal-doped nitride heterojunction catalyst, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the metal-doped nitride heterojunction catalyst according to claim 5 in the preparation of lithium / sodium-sulfur batteries.

7. The application according to claim 6, wherein: Metal-doped nitride heterojunction catalysts are used to prepare positive electrode materials for batteries.

8. A positive electrode material for a lithium / sodium-sulfur battery, which is prepared by mixing the metal-doped nitride heterojunction catalyst according to claim 5 with sulfur and heating the mixture in an argon atmosphere at 155°C, wherein the mass ratio of the metal-doped nitride heterojunction catalyst to sulfur is 2:8 or 3:

7.

9. A lithium-sulfur battery, characterized in that: Prepared by the following method: Preparation of positive electrode material: The metal-doped nitride heterojunction catalyst according to claim 5 and elemental sulfur are placed in an agate mortar at a mass ratio of 2:8, and the mixture is fully ground and mixed, and a constant temperature heat treatment is performed at 155° C. for 12 hours under an argon protective atmosphere to obtain a sulfur positive electrode composite material; Preparation of electrode slurry: The sulfur cathode composite material is mixed with conductive carbon black and polyvinylidene fluoride binder in a mass ratio of 8:1:1, N-methylpyrrolidone solvent is added, and the mixture is continuously stirred for 12 hours by a planetary mixer to obtain a uniformly dispersed electrode slurry; Pole forming and drying: The slurry is evenly coated on the surface of the aluminum foil current collector by a doctor blade coating method, and then the coated pole is placed in a 60°C vacuum drying oven for 12 hours to ensure that the solvent is completely evaporated; Post-processing of pole pieces: Use precision punching machine to process the dry pole pieces into round pole pieces; Battery assembly: The standard CR2032 button battery assembly process was carried out in an argon glove box: the positive electrode shell, sulfur positive electrode plate, 50 μL lithium-sulfur electrolyte, Celgard 2400 polypropylene diaphragm, lithium metal negative electrode plate, stainless steel gasket and negative electrode shell were sequentially loaded and sealed by a hydraulic sealing machine.

10. A sodium-sulfur battery, characterized in that: Prepared by the following method: Preparation of sulfur-based composite material: Using the mechanochemical-melting perfusion method, place the metal-doped nitride heterojunction catalyst described in claim 5 and sublimed sulfur in a mass ratio of 3:7 in an agate mortar and grind for 30 minutes. Under an argon protection atmosphere, heat to 155 °C at a rate of 2 °C / min and perform a 12-hour constant-temperature thermal diffusion treatment to obtain a sulfur-catalyst composite cathode material; Preparation of electrode slurry: Add the sulfur-catalyst composite cathode material, Super P conductive carbon black, and polyvinylidene fluoride binder to a planetary mixer in a mass ratio of 8:1:1, add N-methylpyrrolidone solvent to adjust the slurry viscosity, and continuously stir for 12 hours by the planetary mixer to obtain a uniformly dispersed electrode slurry; Pole piece drying process: Use the doctor blade coating method to uniformly coat the slurry on the surface of the aluminum foil current collector, and then transfer it to a programmable temperature vacuum drying oven. Perform stepwise drying at 60 °C and a vacuum degree of -0.1 MPa: First, rise to 40 °C at a rate of 5 °C / min and maintain for 2 hours to remove the surface solvent, then rise to 60 °C and hold for 10 hours to ensure the volatilization of the deep solvent. Finally, control the water content of the pole piece below 50 ppm; Pole piece forming and quantification: Use a precision punching machine to process the pole piece into a standard round piece; Battery encapsulation: Assemble a CR2032 coin cell in an argon glove box: sequentially place the positive electrode case, sulfur positive electrode pole piece, 120 μL sodium-sulfur electrolyte, Whatman GF / D glass fiber separator, sodium metal negative electrode, spring gasket, and negative electrode case, and seal and form using a hydraulic sealer.

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