IrN2 and Ir nanoparticle composite carbon-based catalyst and its preparation method and application

Abstract

This invention provides an IrN2 and Ir nanoparticle composite carbon-based catalyst, its preparation method, and its application. The preparation method first prepares a zinc-centered zeolite imidazole framework (Zn-ZIF), then coats the Zn-ZIF precursor with dopamine to obtain ZIF@PDA, which is then immersed in an iridium metal salt solution for ion exchange to obtain Ir-ZIF@PDA. Finally, high-temperature calcination yields the IrN2 / Ir composite carbon-based catalyst with the coexistence of IrN2 and Ir nanoparticles. NPs -NC. This material has a simple preparation process, a porous hollow star-shaped structure, and abundant active sites including metals and metal compounds, IrNx, pyridine nitrogen, and pyrrole nitrogen. Modifying the separator with this material using a simple slurry coating method and applying it to lithium-sulfur battery assembly can effectively improve the redox kinetics of sulfur, suppress lithium polysulfide shuttle and volume expansion, thereby achieving high specific capacity and good cycle stability in lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to the field of new chemical energy materials, specifically to an IrN2 and Ir nanoparticle composite carbon-based catalyst, its preparation method, and its application. Background Technology

[0002] With the rapid advancement of socio-economic development and electrification, energy demand continues to rise. Currently, lithium-ion batteries, widely used in daily life, are struggling to meet the ever-expanding energy needs. Lithium-sulfur batteries, with their high theoretical energy density and high theoretical specific capacity, have attracted considerable attention from researchers. Furthermore, sulfur, as a cathode material, possesses significant commercial potential due to its low cost and environmentally friendly characteristics. Therefore, lithium-sulfur batteries are widely considered a strong contender to replace lithium-ion batteries as the next generation of high-energy-density batteries. However, lithium-sulfur batteries currently suffer from problems such as low utilization of sulfur active materials, the "shuttle effect," and volume expansion of intermediate reaction products, ultimately leading to slow sulfur redox kinetics and significant capacity loss.

[0003] Applying carbon-based materials with good conductivity to membrane modification can improve the problem of poor conductivity during charge and discharge. However, the weak physical interaction between carbon materials and polysulfides is insufficient to suppress polysulfide shuttle. Introducing highly polar transition metal compounds onto carbon-based materials can promote charge transfer, and the metal active sites can couple with polysulfides. Effective d-orbital hybridization can enhance the adsorption of polysulfides and improve catalytic activity. However, introducing a single transition metal compound can easily lead to excessive adsorption capacity, ultimately resulting in slow reaction kinetics. Moreover, the catalytic effect of a single type of active site is still insufficient to improve electrochemical performance. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide an IrN2 and Ir nanoparticle composite carbon-based catalyst for the modification of lithium-sulfur battery separators, which can accelerate the lithium-ion transport rate and effectively improve the reaction kinetics of lithium polysulfide conversion, thereby improving the discharge capacity and long-cycle stability of lithium-sulfur batteries.

[0005] First aspect:

[0006] A carbon-based catalyst composed of IrN2 and Ir nanoparticles: IrN2 / Ir NPs -NC is a porous hollow star-shaped structure with a diameter of 400-700 nm, using nitrogen-doped carbon as a support, which loads IrN2 and Ir nanoparticles.

[0007] The composite carbon-based catalyst possesses multiple active sites, including metals and metal compounds, IrNx (iridium nitrogen coordination compounds), pyridine nitrogen, and pyrrole nitrogen. The diversity and abundance of metal active sites ensure interaction with polysulfides, while the edge nitrogen sites such as pyridine nitrogen and pyrrole nitrogen on the nitrogen-doped carbon support improve the material's conductivity and effectively regulate the proportion of IrNx active sites. The introduced multiple catalytic sites effectively modulate the coupling between the metal d orbitals and the polysulfide p orbitals. The porous hollow structure provides a buffer space for the volume expansion and shuttle effect of polysulfides during charge and discharge. The multi-directionally grown 400-700 nm rod-shaped structure resembles a star, with metal nanoparticles uniformly distributed on the surface. Uniform exposure of active sites facilitates sufficient contact between the metal active sites and the polysulfides.

[0008] Second aspect:

[0009] A method for preparing an IrN2 and Ir nanoparticle composite carbon-based catalyst as described in the first aspect includes the following steps:

[0010] Zinc nitrate hexahydrate was dissolved in a dispersant and stirred to form a first solution. Dimethylimidazole and a surfactant were dissolved in the dispersant to form a second solution. The first and second solutions were mixed and stirred, then filtered, washed, and dried to obtain the metal-organic framework Zn-ZIF.

[0011] The Zn-ZIF was placed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and ultrasonically mixed until homogeneous. Then, dopamine hydrochloride was added, and the mixture was stirred again. After filtration, washing, and drying, ZIF@PDA was obtained.

[0012] The ZIF@PDA was dissolved in a dispersant, iridium metal salt was added, and after mixing and stirring, the mixture was filtered and dried to obtain Ir-ZIF@PDA. The Ir-ZIF@PDA was then calcined to obtain the IrN2 / Ir nanoparticle composite carbon-based catalyst. NPs -NC;

[0013] The dispersant includes at least one of deionized water, ethanol, and methanol;

[0014] The surfactant includes at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and ethylene oxide / propylene oxide copolymer (F127);

[0015] The iridium metal salt includes at least one of iridium chloride salt and acetylacetone salt.

[0016] The IrN2 / Ir prepared by this invention NPs-NC possesses a porous and hollow structure. The porous and hollow structure provides a buffer space for the volume expansion and shuttle effect of polysulfides during charge and discharge. Simultaneously, by controlling the amount of external iridium salt added and the rate and temperature of high-temperature calcination, the coexistence of IrN2 and Ir metal nanoparticles, along with nitrogen doping, imbues the catalyst with multiple active sites, including metals and metal compounds, IrNx, pyridine nitrogen, and pyrrole nitrogen. The diversity and abundance of metal active sites ensures interaction with polysulfides, while edge nitrogen sites such as pyridine nitrogen and pyrrole nitrogen improve the material's conductivity and effectively regulate the proportion of IrNx active sites. The introduced multiple catalytic sites effectively modulate the coupling between the material's metal d orbitals and the polysulfide p orbitals. When dp orbital coupling occurs, it enhances electron migration and adsorption strength between the catalyst and polysulfides, thereby improving the kinetics of the adsorption-catalytic reaction.

[0017] In this invention, a zinc-centered zeolite imidazole framework (Zn-ZIF) is first prepared. Then, the Zn-ZIF precursor is coated with dopamine to obtain ZIF@PDA. This ZIF@PDA is then immersed in an iridium metal salt solution for ion exchange to obtain Ir-ZIF@PDA. Finally, high-temperature calcination yields a composite carbon-based catalyst, IrN2 / Ir, containing both IrN2 and Ir nanoparticles. NPs -NC. The preparation process of this invention is relatively simple, the reaction conditions are safe and controllable, and the reactants and products are environmentally friendly. It is expected to put the material into large-scale commercial production, which is of great significance for promoting the commercialization of lithium-sulfur batteries.

[0018] As a preferred embodiment, the first and second solutions are mixed and stirred at 35°C for 3–12 hours. Suitable stirring temperature and time promote the growth of the metal-organic framework Zn-ZIF into rod-like structures in different directions, ultimately forming a star-shaped structure.

[0019] As a preferred embodiment, after adding the dopamine hydrochloride, the mixture is stirred for 3 to 12 hours, then filtered, the filter residue is washed 3 to 5 times, and then placed in a vacuum oven at 50 to 70°C for drying for 6 to 24 hours.

[0020] As a preferred embodiment, the mass ratio of the iridium metal salt to ZIF@PDA is 1:8 to 33. The appropriate addition of the iridium metal salt ensures the uniform distribution of the metal nanoparticles after calcination, preventing metal particle agglomeration that could hinder the formation of reactive sites.

[0021] As a preferred embodiment, the Ir-ZIF@PDA is calcined in an inert gas environment, the inert gas including argon; the calcination conditions are as follows: heating to 800-1000℃ at a heating rate of 0.1-10℃ / min, and holding at that temperature for 2-12 hours.

[0022] An appropriate heating rate is beneficial for the uniform anchoring of the external metal source on the surface, resulting in a more uniform distribution of active sites. Uniform exposure of active sites facilitates full contact between the metal active sites and polysulfides, while also preventing local aggregation of polysulfides. During contact, the d orbitals of the metal active sites couple with the p orbitals of the polysulfides, which is more conducive to the adsorption of intermediate liquid phase polysulfides by the catalyst. Pyrolysis at high temperatures of 800–1000 °C is beneficial for the volatilization of the zinc precursor, while the iridium metal source promotes the breaking of the zinc-dimethylimidazole bond, resulting in a cavity structure in the ZIF and ultimately forming a hollow catalyst material. In addition, high-temperature pyrolysis is beneficial for the generation of metal nanoparticles in which IrN2 and Ir coexist.

[0023] Third aspect:

[0024] A lithium-sulfur battery composite separator is prepared from the IrN2 and Ir nanoparticle composite carbon-based catalyst described in the first aspect.

[0025] Fourth aspect:

[0026] A method for preparing a composite separator for lithium-sulfur batteries as described in the third aspect includes the following steps:

[0027] Using N-methylpyrrolidone as a solvent, the IrN2 and Ir nanoparticle composite carbon-based catalyst is mixed with a conductive agent and a binder, and stirred until homogeneous to form a slurry. The slurry is then uniformly coated onto a commercial separator for lithium-sulfur batteries and dried to obtain the lithium-sulfur battery composite separator.

[0028] A catalyst coating is formed on the surface of an existing separator by simple scraping. This coating can inhibit polysulfide shuttle on the positive electrode side, and the abundant active sites on the surface can also promote the rapid conversion of lithium polysulfides, avoid accumulation on the separator surface, and improve the rate performance of lithium-sulfur batteries. At the same time, the catalyst coating has good lithium affinity and can form a more stable SEI layer, effectively inducing uniform lithium deposition and stripping.

[0029] As a preferred embodiment, the slurry contains, by mass percentage, 70-80% of the composite carbon-based catalyst, 10-20% of the conductive agent, and 5-10% of the binder; the conductive agent includes at least one of conductive carbon black, Ketjen black, and carbon nanotubes; and the material of the commercial lithium-sulfur battery separator includes at least one of Celgard 2400, Celgard 2500, polyethylene separator, and polypropylene separator.

[0030] As a preferred embodiment, the drying conditions are as follows: first, place the product in a forced-air drying oven and dry it at 40-50°C for 3-6 hours, then transfer it to a vacuum drying oven and dry it at 50-70°C for 12-24 hours. Attached Figure Description

[0031] The accompanying drawings are provided to further understand the present technical solution and form part of the specification. They are used together with the embodiments of the present technical solution to explain the present technical solution and do not constitute a limitation on the present technical solution.

[0032] Figure 1 It is the IrN2 / Ir prepared in Example 1 of this invention. NPs - Scanning electron microscope (SEM) image of the NC material; among which, Figure 1 a and Figure 1 b represents the same IrN2 / Ir NPs -SEM images of NC materials at different magnifications;

[0033] Figure 2 It is the IrN2 / Ir prepared in Example 1 of this invention. NPs -Scanning electron microscope (SEM) image of a modified separator cross section after NC material is coated onto a commercial lithium-sulfur separator;

[0034] Figure 3 It is the IrN2 / Ir prepared in Example 1 of this invention. NPs - Transmission electron microscopy (TEM) image of NC material;

[0035] Figure 4 These are charge-discharge performance graphs at different rates when the modified separators prepared in Embodiment 1 and Comparative Example 1 and the unmodified separator in Comparative Example 2 are applied to lithium-sulfur batteries. Detailed Implementation

[0036] The preferred embodiments of this technical solution are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only for illustration and explanation of this technical solution and are not intended to limit this technical solution.

[0037] (1) Preparation of metal-organic framework Zn-ZIF

[0038] Zinc nitrate hexahydrate is dissolved in a dispersant and stirred to form a first solution. Dimethylimidazole and a surfactant are dissolved in the dispersant to form a second solution. The first and second solutions are mixed and stirred at 35°C for 3–12 h. After filtration, washing, and drying, the metal-organic framework Zn-ZIF is obtained. The dispersant includes at least one of deionized water, ethanol, and methanol; the surfactant includes at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and ethylene oxide / propylene oxide copolymer (F127).

[0039] (2) Preparation of dopamine-coated ZIF@PDA

[0040] The Zn-ZIF obtained in step (1) was placed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and ultrasonically mixed. Then, dopamine hydrochloride was added and the mixture was stirred for 3 to 12 hours. After that, the mixture was filtered and the filter residue was washed 3 to 5 times. Then, it was placed in a vacuum oven at 50 to 70°C and dried for 6 to 24 hours to obtain ZIF@PDA.

[0041] (3) Preparation of IrN2 and Ir nanoparticle composite carbon-based catalyst IrN2 / Ir NPs -NC

[0042] The ZIF@PDA obtained in step (2) is dissolved in a dispersant, and an iridium metal salt is added. The mass ratio of the iridium metal salt to ZIF@PDA is 1:8 to 33. After mixing and stirring evenly, the mixture is filtered and dried to obtain Ir-ZIF@PDA. The Ir-ZIF@PDA is placed in a tube furnace, and an inert gas is introduced for 1 hour to remove air. Then, the temperature is increased to 800 to 1000°C at a heating rate of 0.1 to 10°C / min, and held for 2 to 12 hours. After high-temperature calcination, IrN2 / Ir is obtained. NPs -NC material. The iridium metal salt includes at least one of iridium chloride and acetylacetonate.

[0043] (4) Preparation of membrane modified with IrN2 and Ir nanoparticle composite carbon-based catalyst

[0044] Using N-methylpyrrolidone as a solvent, the IrN2 and Ir nanoparticle composite carbon-based catalyst obtained in step (3) is mixed with a conductive agent and a binder, and stirred until homogeneous to form a slurry. The slurry is then uniformly coated onto a commercial separator for lithium-sulfur batteries, dried in a forced-air drying oven at 40–50°C for 3–6 hours, and then transferred to a vacuum drying oven at 50–70°C for 12–24 hours. The composite carbon-based catalyst accounts for 70–80%, the conductive agent accounts for 10–20%, and the binder accounts for 5–10%. The conductive agent includes at least one of conductive carbon black, Ketjen black, and carbon nanotubes. The material of the commercial separator for lithium-sulfur batteries includes at least one of Celgard 2400, Celgard 2500, polyethylene separator, and polypropylene separator.

[0045] (5) Preparation of sulfur composite cathode

[0046] Carbon nanotubes and sulfur were mixed at a mass ratio of 7:3 and thoroughly ground. The mixture was then heat-treated in an oven at 155°C for 12 hours to obtain a carbon / sulfur composite material. The carbon / sulfur composite material, Super P, and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1 and stirred until homogeneous. The slurry was then evenly coated onto aluminum foil using a 200 μm scraper, and subsequently dried in a forced-air drying oven at 50°C for 6 hours. Finally, it was transferred to a vacuum drying oven at 70°C for 12 hours to obtain a sulfur composite cathode.

[0047] (6) Assembly of lithium-sulfur batteries

[0048] The sulfur composite cathode prepared in step (5) was used as the positive electrode, the lithium metal sheet as the negative electrode, and the IrN2 and Ir nanoparticle composite carbon-based catalyst modified membrane prepared in step (4) was used as the battery separator. The electrolyte was a lithium-sulfur electrolyte prepared with 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and 1% lithium nitrate by mass. The CR2025 button cell was assembled in a glove box under an argon atmosphere. The assembled battery was subjected to constant current charge-discharge tests using a Newway testing system, with a voltage range of 1.5–3V.

[0049] Example 1

[0050] (1) Preparation of metal-organic framework Zn-ZIF

[0051] First, 0.6 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added to 20 ml of deionized water and sonicated for about 30 seconds to dissolve it evenly into a clear and transparent solution, forming the first solution. Then, 3.280 g of dimethylimidazole (C4H6N2) and 0.01 g of hexadecyltrimethylammonium bromide (CTAB) were added to 80 ml of deionized water and stirred for about 30 seconds to dissolve it into a clear and transparent solution, forming the second solution. The first solution was quickly poured into the second solution, and then the mixture was placed on a magnetic stirrer and stirred at 500 rpm at 35°C for 4 hours. After centrifugation and filtration, a white precipitate was obtained. The white precipitate was washed three times with deionized water and finally dried in a vacuum oven at 70°C for 12 hours to obtain the metal-organic framework Zn-ZIF.

[0052] (2) Preparation of dopamine-coated ZIF@PDA

[0053] 0.3g of Zn-ZIF obtained in step (1) was added to 60ml of Tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution and sonicated for 30min to mix it evenly, resulting in a white emulsion solution. 0.15g of polydopamine hydrochloride was added to the white emulsion solution, and then the mixture was placed on a magnetic stirrer and stirred at 500rpm at room temperature for 12h. After centrifugation and filtration, a black precipitate was obtained. The black precipitate was washed 5 times with deionized water and then dried in a vacuum oven at 70℃ for 12h to obtain the metal-organic framework ZIF@PDA.

[0054] (3) Preparation of IrN2 and Ir nanoparticle composite carbon-based catalyst IrN2 / Ir NPs -NC

[0055] 0.2 g of ZIF@PDA obtained in step (2) was added to 25 ml of ethanol solution and sonicated for 1 min to mix evenly, resulting in a black solution. 12 mg of iridium chloride trihydrate (IrCl3·3H2O) was added to the black solution and stirred for 6 h. The mixture was centrifuged and filtered to obtain a black precipitate, which was then dried in a vacuum oven at 70 °C for 5 h to obtain Ir-ZIF@PDA. The Ir-ZIF@PDA was placed in a tube furnace and inert gas was introduced for 1 h to remove air. The temperature was then increased to 900 °C at a rate of 5 °C / min and held for 2 h. After high-temperature calcination, IrN2 / Ir was obtained. NPs -NC material.

[0056] (4) Preparation of membrane modified with IrN2 and Ir nanoparticle composite carbon-based catalyst

[0057] The IrN2 / Ir obtained in step (3) NPs -NC material is mixed with Super P and PVDF at a mass ratio of 7:2:1 to obtain a uniform slurry. The slurry is then uniformly coated onto a polypropylene membrane using a 50μm scraper. After that, it is placed in a forced-air drying oven at 50℃ for 6 hours and then transferred to a vacuum drying oven at 70℃ for 12 hours to obtain a membrane modified with IrN2 and Ir nanoparticle composite carbon-based catalyst.

[0058] (5) Preparation of sulfur composite cathode

[0059] Carbon nanotubes and sulfur were mixed at a mass ratio of 7:3 and thoroughly ground. The mixture was then heat-treated in an oven at 155°C for 12 hours to obtain a carbon / sulfur composite material. The carbon / sulfur composite material, Super P, and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1 and stirred until homogeneous. The slurry was then evenly coated onto aluminum foil using a 200 μm scraper, and subsequently dried in a forced-air drying oven at 50°C for 6 hours. Finally, it was transferred to a vacuum drying oven at 70°C for 12 hours to obtain a sulfur composite cathode.

[0060] (6) Assembly of lithium-sulfur batteries

[0061] The sulfur composite cathode prepared in step (5) was used as the positive electrode, the lithium metal sheet as the negative electrode, and the IrN2 and Ir nanoparticle composite carbon-based catalyst modified membrane prepared in step (4) was used as the battery separator. The electrolyte was a lithium-sulfur electrolyte prepared with 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and 1% lithium nitrate by mass. The CR2025 button cell was assembled in a glove box under an argon atmosphere. The assembled battery was subjected to constant current charge-discharge tests using a Newway testing system, with a voltage range of 1.5–3V.

[0062] from Figure 1 The scanning electron microscope image of a shows IrN2 / Ir NPs -NC exhibits a hollow star-shaped structure with a size of approximately 600nm. Figure 1 b shows the morphology of the catalyst at a higher resolution, revealing the cavity structure and the formation of pointed rods.

[0063] Figure 2 Demonstrates the use of IrN2 / Ir NPs -Cross-sectional view of NC catalyst coated on a commercial membrane. The catalyst retains its original morphology after being attached to the commercial membrane, and the coating is uniform with a thickness of 9 μm.

[0064] Figure 3 The transmission electron microscope (TEM) images further clearly show the IrN2 / Ir ratio. NPs The hollow structure inside the NC and the absence of obvious IrN2 and Ir metal particle agglomeration on the surface indicate that the metal particles are uniformly dispersed.

[0065] Example 2

[0066] (1) Preparation of metal-organic framework Zn-ZIF

[0067] First, 0.6 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added to 20 ml of deionized water and sonicated for about 30 seconds to dissolve it evenly into a clear and transparent solution, forming the first solution. Then, 3.280 g of dimethylimidazole (C4H6N2) and 0.01 g of dodecyltrimethylammonium bromide were added to 80 ml of deionized water and stirred for about 30 seconds to dissolve it into a clear and transparent solution, forming the second solution. The first solution was quickly poured into the second solution, and then placed on a magnetic stirrer and stirred at 500 rpm at 35°C for 12 h. After centrifugation and filtration, a white precipitate was obtained. The white precipitate was washed three times with deionized water and finally dried in a vacuum oven at 70°C for 12 h to obtain the metal-organic framework Zn-ZIF.

[0068] (2) Preparation of dopamine-coated ZIF@PDA

[0069] 0.3g of Zn-ZIF obtained in step (1) was added to 60ml of Tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution and sonicated for 30min to mix it evenly, resulting in a white emulsion solution. 0.15g of polydopamine hydrochloride was added to the white emulsion solution, and then the mixture was placed on a magnetic stirrer and stirred at 500rpm at room temperature for 12h. After centrifugation and filtration, a black precipitate was obtained. The black precipitate was washed 5 times with deionized water and then dried in a vacuum oven at 50℃ for 24h to obtain the metal-organic framework ZIF@PDA.

[0070] (3) Preparation of IrN2 and Ir nanoparticle composite carbon-based catalyst IrN2 / Ir NPs -NC

[0071] 0.2 g of ZIF@PDA obtained in step (2) was added to 25 ml of ethanol solution and sonicated for 1 min to mix evenly, resulting in a black solution. 24 mg of iridium chloride trihydrate (IrCl3·3H2O) was added to the black solution and stirred for 6 h. The mixture was centrifuged and filtered to obtain a black precipitate, which was then dried in a vacuum oven at 70 °C for 5 h to obtain Ir-ZIF@PDA. Ir-ZIF@PDA was placed in a tube furnace and inert gas was introduced for 1 h to remove air. The temperature was then increased to 1000 °C at a rate of 10 °C / min and held for 4 h. After high-temperature calcination, IrN2 / Ir was obtained. NPs -NC material.

[0072] (4) Preparation of membranes modified with IrN2 and Ir nanoparticle composite carbon-based catalysts:

[0073] The IrN2 / Ir obtained in step (3) NPs-NC material is mixed with Super P and PVDF at a mass ratio of 7:2:1 to obtain a uniform slurry. The slurry is then uniformly coated onto a polypropylene membrane using a 50μm scraper. After that, it is placed in a forced-air drying oven at 50℃ for 6 hours and then transferred to a vacuum drying oven at 70℃ for 12 hours to obtain a membrane modified with IrN2 and Ir nanoparticle composite carbon-based catalyst.

[0074] (5) Preparation of sulfur composite cathode

[0075] Carbon nanotubes and sulfur were mixed at a mass ratio of 7:3 and thoroughly ground, then heat-treated in an oven at 155℃ for 12 hours to obtain a carbon / sulfur composite material. The carbon / sulfur composite material, Super P, and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1 and stirred until homogeneous. The slurry was then evenly coated onto aluminum foil using a 200μm scraper, and subsequently dried in a forced-air drying oven at 40℃ for 3 hours. Finally, it was transferred to a vacuum drying oven at 50℃ for 24 hours to obtain a sulfur composite cathode.

[0076] (6) Assembly of lithium-sulfur batteries

[0077] The sulfur composite cathode prepared in step (5) was used as the positive electrode, the lithium metal sheet as the negative electrode, and the IrN2 and Ir nanoparticle composite carbon-based catalyst modified membrane prepared in step (4) was used as the battery separator. The electrolyte was a lithium-sulfur electrolyte prepared with 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and 1% lithium nitrate by mass. The CR2025 button cell was assembled in a glove box under an argon atmosphere. The assembled battery was subjected to constant current charge-discharge tests using a Newway testing system, with a voltage range of 1.5–3V.

[0078] Example 3

[0079] (1) Preparation of metal-organic framework Zn-ZIF

[0080] First, 0.6 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added to 20 ml of deionized water and sonicated for about 30 seconds to dissolve it evenly into a clear and transparent solution, forming the first solution. Then, 3.280 g of dimethylimidazole (C4H6N2) and 0.01 g of ethylene oxide / propylene oxide copolymer (F127) were added to 80 ml of deionized water and stirred for about 30 seconds to dissolve it into a clear and transparent solution, forming the second solution. The first solution was quickly poured into the second solution, and then the mixture was placed on a magnetic stirrer and stirred at 500 rpm at 35°C for 4 hours. After centrifugation and filtration, a white precipitate was obtained. The white precipitate was washed three times with deionized water and finally dried in a vacuum oven at 70°C for 12 hours to obtain the metal-organic framework Zn-ZIF.

[0081] (2) Preparation of dopamine-coated ZIF@PDA

[0082] 0.3g of Zn-ZIF obtained in step (1) was added to 60ml of Tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution and sonicated for 30min to mix it evenly, resulting in a white emulsion solution. 0.15g of polydopamine hydrochloride was added to the white emulsion solution, and then the mixture was placed on a magnetic stirrer and stirred at 500rpm at room temperature for 12h. After centrifugation and filtration, a black precipitate was obtained. The precipitate was washed three times with deionized water and then dried in a vacuum oven at 70℃ for 6h to obtain the metal-organic framework ZIF@PDA.

[0083] (3) Preparation of IrN2 and Ir nanoparticle composite carbon-based catalyst IrN2 / Ir NPs -NC

[0084] 0.2 g of ZIF@PDA obtained in step (2) was added to 25 ml of ethanol solution and sonicated for 1 min to mix evenly, resulting in a black solution. 6 mg of iridium chloride trihydrate (IrCl3·3H2O) was added to the black solution and stirred for 6 h. The mixture was centrifuged and filtered to obtain a black precipitate, which was then dried in a vacuum oven at 70 °C for 5 h to obtain Ir-ZIF@PDA. The Ir-ZIF@PDA was placed in a tube furnace and inert gas was introduced for 1 h to remove air. The temperature was then increased to 800 °C at a rate of 1 °C / min and held for 12 h. After high-temperature calcination, IrN2 / Ir was obtained. NPs -NC material.

[0085] (4) Preparation of membranes modified with IrN2 and Ir nanoparticle composite carbon-based catalysts:

[0086] The IrN2 / Ir obtained in step (3) NPs-NC material is mixed with Super P and PVDF at a mass ratio of 7:2:1 to obtain a uniform slurry. The slurry is then uniformly coated onto a polypropylene membrane using a 50μm scraper. After that, it is placed in a forced-air drying oven at 40℃ for 3 hours and then transferred to a vacuum drying oven at 50℃ for 24 hours to obtain a membrane modified with IrN2 and Ir nanoparticle composite carbon-based catalyst.

[0087] (5) Preparation of sulfur composite cathode

[0088] Carbon nanotubes and sulfur were mixed at a mass ratio of 7:3 and thoroughly ground. The mixture was then heat-treated in an oven at 155°C for 12 hours to obtain a carbon / sulfur composite material. The carbon / sulfur composite material, Super P, and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1 and stirred until homogeneous. The slurry was then evenly coated onto aluminum foil using a 200 μm scraper, and subsequently dried in a forced-air drying oven at 50°C for 6 hours. Finally, it was transferred to a vacuum drying oven at 70°C for 12 hours to obtain a sulfur composite cathode.

[0089] (6) Assembly of lithium-sulfur batteries

[0090] The sulfur composite cathode prepared in step (5) was used as the positive electrode, the lithium metal sheet as the negative electrode, and the IrN2 and Ir nanoparticle composite carbon-based catalyst modified membrane prepared in step (4) was used as the battery separator. The electrolyte was a lithium-sulfur electrolyte prepared with 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and 1% lithium nitrate by mass. The CR2025 button cell was assembled in a glove box under an argon atmosphere. The assembled battery was subjected to constant current charge-discharge tests using a Newway testing system, with a voltage range of 1.5–3V.

[0091] Example 4

[0092] (1) Preparation of metal-organic framework Zn-ZIF

[0093] First, 0.6 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added to 20 ml of deionized water and sonicated for about 30 seconds to dissolve it evenly into a clear and transparent solution, forming the first solution. Then, 3.280 g of dimethylimidazole (C4H6N2) and 0.01 g of hexadecyltrimethylammonium bromide (CTAB) were added to 80 ml of deionized water and stirred for about 30 seconds to dissolve it into a clear and transparent solution, forming the second solution. The first solution was quickly poured into the second solution, and then the mixture was placed on a magnetic stirrer and stirred at 500 rpm at 35°C for 4 hours. After centrifugation and filtration, a white precipitate was obtained. The white precipitate was washed three times with deionized water and finally dried in a vacuum oven at 70°C for 12 hours to obtain the metal-organic framework Zn-ZIF.

[0094] (2) Preparation of dopamine-coated ZIF@PDA

[0095] 0.3g of Zn-ZIF obtained in step (1) was added to 60ml of Tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution and sonicated for 30min to mix it evenly, resulting in a white emulsion solution. 0.15g of polydopamine hydrochloride was added to the white emulsion solution, and then the mixture was placed on a magnetic stirrer and stirred at 500rpm at room temperature for 12h. After centrifugation and filtration, a black precipitate was obtained. The black precipitate was washed 5 times with deionized water and then dried in a vacuum oven at 70℃ for 12h to obtain the metal-organic framework ZIF@PDA.

[0096] (3) Preparation of IrN2 and Ir nanoparticle composite carbon-based catalyst IrN2 / Ir NPs -NC

[0097] 0.2 g of ZIF@PDA obtained in step (2) was added to 25 ml of ethanol solution and sonicated for 1 min to mix evenly, resulting in a black solution. 12 mg of iridium acetylacetone (Ir(acac)3) was added to the black solution and stirred for 6 h. The mixture was centrifuged and filtered to obtain a black precipitate, which was then dried in a vacuum oven at 70 °C for 5 h to obtain Ir-ZIF@PDA. The Ir-ZIF@PDA was placed in a tube furnace and inert gas was introduced for 1 h to remove air. The temperature was then increased to 900 °C at a rate of 0.1 °C / min and held for 6 h. After high-temperature calcination, IrN2 / Ir was obtained. NPs -NC material.

[0098] (4) Preparation of membranes modified with IrN2 and Ir nanoparticle composite carbon-based catalysts:

[0099] The IrN2 / Ir obtained in step (3) NPs-NC material is mixed with Super P and PVDF at a mass ratio of 7:2:1 to obtain a uniform slurry. The slurry is then uniformly coated onto a polypropylene membrane using a 50μm scraper. After that, it is placed in a forced-air drying oven at 50℃ for 6 hours and then transferred to a vacuum drying oven at 70℃ for 12 hours to obtain a membrane modified with IrN2 and Ir nanoparticle composite carbon-based catalyst.

[0100] (5) Preparation of sulfur composite cathode

[0101] Carbon nanotubes and sulfur were mixed at a mass ratio of 7:3 and thoroughly ground. The mixture was then heat-treated in an oven at 155°C for 12 hours to obtain a carbon / sulfur composite material. The carbon / sulfur composite material, Super P, and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1 and stirred until homogeneous. The slurry was then evenly coated onto aluminum foil using a 200 μm scraper, and subsequently dried in a forced-air drying oven at 50°C for 6 hours. Finally, it was transferred to a vacuum drying oven at 70°C for 12 hours to obtain a sulfur composite cathode.

[0102] (6) Assembly of lithium-sulfur batteries

[0103] The sulfur composite cathode prepared in step (5) was used as the positive electrode, the lithium metal sheet as the negative electrode, and the IrN2 and Ir nanoparticle composite carbon-based catalyst modified membrane prepared in step (4) was used as the battery separator. The electrolyte was a lithium-sulfur electrolyte prepared with 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and 1% lithium nitrate by mass. The CR2025 button cell was assembled in a glove box under an argon atmosphere. The assembled battery was subjected to constant current charge-discharge tests using a Newway testing system, with a voltage range of 1.5–3V.

[0104] Comparative Example 1

[0105] (1) Preparation of metal-organic framework Zn-ZIF

[0106] First, 0.6 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added to 20 ml of deionized water and sonicated for about 30 seconds to dissolve it evenly into a clear and transparent solution, forming the first solution. Then, 3.280 g of dimethylimidazole (C4H6N2) and 0.01 g of hexadecyltrimethylammonium bromide (CTAB) were added to 80 ml of deionized water and stirred for about 30 seconds to dissolve it into a clear and transparent solution, forming the second solution. The first solution was quickly poured into the second solution, and then the mixture was placed on a magnetic stirrer and stirred at 500 rpm at 35°C for 4 hours. After centrifugation and filtration, a white precipitate was obtained. The white precipitate was washed three times with deionized water and finally dried in a vacuum oven at 70°C for 12 hours to obtain the metal-organic framework Zn-ZIF.

[0107] (2) Preparation of dopamine-coated ZIF@PDA

[0108] 0.3g of Zn-ZIF obtained in step (1) was added to 60ml of Tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution and sonicated for 30min to mix it evenly, resulting in a white emulsion solution. 0.15g of polydopamine hydrochloride was added to the white emulsion solution, and then the mixture was placed on a magnetic stirrer and stirred at 500rpm at room temperature for 12h. After centrifugation and filtration, a black precipitate was obtained. The black precipitate was washed 5 times with deionized water and then dried in a vacuum oven at 70℃ for 12h to obtain the metal-organic framework ZIF@PDA.

[0109] (3) Preparation of nitrogen-doped carbon composite catalyst NC

[0110] The ZIF@PDA obtained in step (2) was placed in a tube furnace and inert gas was introduced for 1 hour to remove air. Then, the temperature was increased to 900°C at a rate of 5°C / min and held for 2 hours. After high-temperature calcination, NC material was obtained.

[0111] (4) Preparation of nitrogen-doped carbon-modified membranes:

[0112] The NC material obtained in step (3) was mixed with Super P and PVDF at a mass ratio of 7:2:1 to obtain a uniform slurry. The slurry was then uniformly coated onto the polypropylene membrane using a 50 μm scraper. After that, it was placed in a forced-air drying oven for drying at 50°C for 6 hours. Then, it was transferred to a vacuum drying oven at 70°C for 12 hours to obtain a nitrogen-doped carbon-modified membrane.

[0113] (5) Preparation of sulfur composite cathode

[0114] Carbon nanotubes and sulfur were mixed at a mass ratio of 7:3 and thoroughly ground. The mixture was then heat-treated in an oven at 155°C for 12 hours to obtain a carbon / sulfur composite material. The carbon / sulfur composite material, Super P, and PVDF were then added to an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1 and stirred until homogeneous. The slurry was then evenly coated onto aluminum foil using a 200 μm scraper, and subsequently dried in a forced-air drying oven at 50°C for 6 hours. Finally, it was transferred to a vacuum drying oven at 70°C for 12 hours to obtain a sulfur composite cathode.

[0115] (6) Assembly of lithium-sulfur batteries

[0116] The sulfur composite cathode prepared in step (5) was used as the positive electrode, the lithium metal sheet as the negative electrode, and the nitrogen-doped carbon-modified separator prepared in step (4) as the battery separator. The electrolyte was a lithium-sulfur electrolyte prepared with 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1 and 1% lithium nitrate by mass. CR2025 button batteries were assembled in an argon-atmosphere glove box. The assembled batteries were subjected to constant current charge-discharge tests using a Newway testing system, with a voltage range of 1.5–3V.

[0117] Comparative Example 2

[0118] This comparative example uses an unmodified Celgard 2400 separator. The preparation of the sulfur composite cathode and the assembly of the lithium-sulfur battery are the same as in Example 1.

[0119] Effect verification

[0120] The modified membranes prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to electrochemical performance tests on the Xinwei testing system. The test voltage range was 1.5-3V, and the test results are shown in Table 1.

[0121] Table 1. First-cycle discharge specific capacity and long-cycle performance of batteries assembled in Examples 1-4 and Comparative Examples 1-2.

[0122]

[0123] As can be seen from Table 1, IrN2 / Ir NPs The coin cell assembled with an NC-modified separator exhibits a significantly higher first-cycle discharge specific capacity at 0.2C rate than comparative examples 1-2; at 2C rate, the IrN2 / Ir... NPs The coin cell assembled with the NC-modified separator had a better first-cycle discharge specific capacity than Comparative Example 2 and was similar to Comparative Example 1. However, Comparative Example 1 had poor long-cycle stability and failed before 600 cycles.

[0124] from Figure 4 It can be seen that, from IrN2 / Ir NPs Coin cells assembled with NC-modified separators exhibit the most stable capacity retention and high specific capacity at different current densities. The first-cycle discharge specific capacities at current densities of 0.2C, 0.5C, 1.0C, and 2.0C are 1650, 1171, 1065, and 948 mAh g, respectively. -1 Compared with the NC material-modified separator of Comparative Example 1 and the unmodified separator of Comparative Example 2, it can be seen that IrN2 / Ir NPs -NC-modified separators can effectively improve the rate performance of lithium-sulfur batteries.

Claims

1. A carbon-based catalyst composed of IrN2 and Ir nanoparticles: IrN2 / Ir NPs -NC, characterized in that, A porous hollow star-shaped structure composed of rod-like structures of 400-700 nm is used as a support for nitrogen-doped carbon, which includes pyridine nitrogen and pyrrole nitrogen, and IrN2 and Ir nanoparticles are loaded on the support.

2. A method for preparing the IrN2 and Ir nanoparticle composite carbon-based catalyst as described in claim 1, comprising the following steps: Zinc nitrate hexahydrate was dissolved in a dispersant and stirred to form a first solution. Dimethylimidazole and a surfactant were dissolved in the dispersant to form a second solution. The first and second solutions were mixed and stirred, then filtered, washed, and dried to obtain the metal-organic framework Zn-ZIF. The Zn-ZIF was placed in a tris(hydroxymethyl)aminomethane hydrochloride buffer solution and ultrasonically mixed until homogeneous. Then, dopamine hydrochloride was added, and the mixture was stirred again. After filtration, washing, and drying, ZIF@PDA was obtained. The ZIF@PDA was dissolved in a dispersant, iridium metal salt was added, and after mixing and stirring, the mixture was filtered and dried to obtain Ir-ZIF@PDA. The Ir-ZIF@PDA was then calcined to obtain the IrN2 / Ir nanoparticle composite carbon-based catalyst. NPs -NC; The dispersant includes at least one of deionized water, ethanol, and methanol; The surfactant includes at least one of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and ethylene oxide / propylene oxide copolymer; The iridium metal salt includes at least one of iridium chloride salt and acetylacetone salt.

3. The method for preparing the IrN2 and Ir nanoparticle composite carbon-based catalyst according to claim 2, characterized in that, The first solution and the second solution are mixed and stirred at a temperature of 35°C for 3 to 12 hours.

4. The method for preparing the IrN2 and Ir nanoparticle composite carbon-based catalyst according to claim 2, characterized in that, After adding the dopamine hydrochloride, stir and mix for 3 to 12 hours, then filter, wash the filter residue 3 to 5 times, and then place it in a vacuum oven at 50 to 70°C to dry for 6 to 24 hours.

5. The method for preparing the IrN2 and Ir nanoparticle composite carbon-based catalyst according to claim 2, characterized in that, The mass ratio of the iridium metal salt to ZIF@PDA is 1:8 to 33.

6. The method for preparing the IrN2 and Ir nanoparticle composite carbon-based catalyst according to claim 2, characterized in that, The Ir-ZIF@PDA is calcined in an inert gas environment, the inert gas including argon; the calcination conditions are as follows: heating to 800-1000℃ at a heating rate of 0.1-10℃ / min, and holding at that temperature for 2-12 hours.

7. A lithium-sulfur battery composite separator, prepared from the IrN2 and Ir nanoparticle composite carbon-based catalyst as described in claim 1.

8. A method for preparing a lithium-sulfur battery composite separator as described in claim 7, comprising the following steps: Using N-methylpyrrolidone as a solvent, the IrN2 and Ir nanoparticle composite carbon-based catalyst is mixed with a conductive agent and a binder, and stirred until homogeneous to form a slurry. The slurry is then uniformly coated onto a commercial separator for lithium-sulfur batteries and dried to obtain the lithium-sulfur battery composite separator.

9. The method for preparing the lithium-sulfur battery composite separator according to claim 8, characterized in that, The slurry contains, by mass percentage, 70-80% of the IrN2 and Ir nanoparticle composite carbon-based catalyst, 10-20% of the conductive agent, and 5-10% of the binder; the conductive agent includes at least one of conductive carbon black, Ketjen black, and carbon nanotubes; the material of the commercial lithium-sulfur battery separator includes at least one of Celgard 2400, Celgard 2500, polyethylene separator, and polypropylene separator.

10. The method for preparing the lithium-sulfur battery composite separator according to claim 8, characterized in that, The drying conditions are as follows: first, place the product in a forced-air drying oven at 40-50°C for 3-6 hours, and then transfer it to a vacuum drying oven at 50-70°C for 12-24 hours.

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