A metal nanoparticle-loaded porous carbon material, a preparation method therefor, and an application thereof

Abstract

The application relates to the technical field of batteries, and particularly discloses a metal nanoparticle-loaded porous carbon material, a preparation method and application thereof. The preparation method of the metal nanoparticle-loaded porous carbon material comprises the following steps: dispersing MOF in a metal salt solution, then activating at high temperature, and separating the solid phase after activation to obtain a metal ion-doped MOF precursor; and carbonizing the metal ion-doped MOF precursor in a magnetic field to obtain the metal nanoparticle-loaded porous carbon material. The synergistic effect of high-temperature activation and magnetic field carbonization realizes precise control of cross-scale from atomic-level doping to nanometer-level directional assembly, and the metal nanoparticle-loaded porous carbon material with high-density active sites and excellent conductivity is prepared. The lithium-sulfur battery prepared by using the material has excellent initial capacity and cycle stability, and can be well applied in the fields of portable electronic devices, electric vehicles, unmanned aerial vehicles or energy storage systems.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a porous carbon material loaded with metal nanoparticles, its preparation method, and its application. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, drones, and large-scale energy storage systems, society is placing increasingly higher demands on the energy density, safety, and economy of rechargeable batteries. Lithium-sulfur batteries are a type of lithium battery that uses sulfur as the positive electrode and metallic lithium as the negative electrode. Their working principle is based on the multi-electron redox reaction of sulfur. Lithium-sulfur batteries using sulfur as the positive electrode material have high theoretical specific capacity and theoretical specific energy, reaching 1675 mAh / g and 2600 Wh / kg respectively, far exceeding the capacity of commercially widely used lithium cobalt oxide batteries (less than 150 mAh / g). Furthermore, sulfur, an active material, is abundant in the Earth's crust, inexpensive, and environmentally friendly. Therefore, lithium-sulfur batteries, with their extremely high theoretical energy density and excellent cost advantages, are considered one of the most promising development directions for next-generation high-energy-density rechargeable batteries.

[0003] However, although lithium-sulfur batteries have great theoretical potential, their sulfur cathode materials have inherent defects in practical applications, mainly including the following aspects: (1) the soluble lithium polysulfides generated during charging and discharging will cause a serious "shuttle effect", resulting in loss of active materials, capacity decay and low coulombic efficiency; (2) sulfur and its discharge products have extremely poor conductivity, which restricts reaction kinetics and rate performance; (3) the volume expansion of sulfur in the reaction of about 80% will destroy the integrity of the electrode structure and affect the cycle life.

[0004] To address these issues, researchers both domestically and internationally have conducted extensive research. In cathode modification, the main strategies include combining sulfur with porous carbon materials (such as graphene, carbon nanotubes, and mesoporous carbon), utilizing the conductivity of carbon materials to improve electron transport, and relying on their physical confinement effect to suppress polysulfide diffusion. While current mainstream sulfur-support designs can physically confine sulfur and improve conductivity to some extent, their chemical anchoring ability for lithium polysulfides is insufficient, and their effect on suppressing the "shuttle effect" is limited, resulting in poor cycle life and coulombic efficiency. Furthermore, complex structural materials with excellent performance often have complex fabrication processes and high costs, making it difficult to meet the comprehensive requirements of long battery life, high reliability, and industrial cost control. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the first objective of the present invention is to provide a method for preparing a porous carbon material loaded with metal nanoparticles. The second objective of the present invention is to provide a porous carbon material loaded with metal nanoparticles obtained by this preparation method. The third objective of the present invention is to provide applications of this porous carbon material loaded with metal nanoparticles.

[0006] The inventive concept of this invention is as follows: Metal ions are doped into the channels of a metal-organic framework (MOF). High-temperature liquid-phase activation is used to enable the metal ions to diffuse into the interior of the MOF framework efficiently and uniformly. Then, under the induction of a magnetic field, high-temperature carbonization reduces the doped metal ions into uniformly and orderly dispersed metal nanoparticles. The organic part of the MOF is carbonized to form a porous carbon material, thereby obtaining a porous carbon material loaded with metal nanoparticles.

[0007] To achieve the first objective mentioned above, the present invention provides the following technical solution.

[0008] In a first aspect, the present invention provides a method for preparing porous carbon materials loaded with metal nanoparticles, comprising the following steps: S1: Disperse MOF in a metal salt solution, then activate it at high temperature, and separate the solid phase after activation to obtain a metal ion-doped MOF precursor. S2: Carbonize the metal ion-doped MOF precursor described in step S1 in a magnetic field to obtain the porous carbon material loaded with metal nanoparticles.

[0009] This invention adsorbs metal ions from a metal salt solution within the porous framework structure of a metal-oxide-semiconductor (MOF). High-temperature activation efficiently and uniformly disperses these metal ions within the pores of the MOF framework, achieving atomic-level metal ion doping in the resulting metal-MOF precursor. Then, carbonization in a magnetic field reduces the uniformly distributed metal ions (including post-doped and pre-doped metal ions from the MOF) in the metal-MOF precursor to metal nanoparticles, achieving ordered dispersion of the nanoparticles. The organic portion of the metal-MOF precursor carbonizes to form a porous carbon material, thus yielding a porous carbon material loaded with metal nanoparticles. In this invention, high-temperature activation improves the permeability of the pore structure within the MOF framework, ensuring high uniformity of the chemical composition (metal ions) within the MOF framework. After carbonization in the magnetic field, an ordered and oriented magnetic conductive network is formed within the MOF, preventing the collapse of the porous carbon framework and the aggregation of nanoparticles after carbonization. The synergistic effect of high-temperature activation and magnetic field carbonization in this invention enables precise control across scales, from atomic-level doping to nanoscale directional assembly, and prepares porous carbon materials with both high-density active sites and excellent conductivity, loaded with metal nanoparticles.

[0010] Preferably, the size of the metal nanoparticles supported on the porous carbon material is 10~30nm; more preferably, the size of the metal nanoparticles supported on the porous carbon material is 12~28nm; and even more preferably, the size of the metal nanoparticles supported on the porous carbon material is 15~25nm.

[0011] Preferably, the MOF includes ZIF-67.

[0012] Preferably, the ZIF-67 is prepared by the following method: a solution containing cobalt ions is mixed with a solution containing 2-methylimidazole to obtain a ZIF-67 precursor solution, and then the ZIF-67 precursor solution is allowed to stand for aging and the precipitate is separated to obtain the ZIF-67.

[0013] Preferably, the metal salt includes at least one of iron salt and nickel salt.

[0014] Preferably, the metal salt includes at least one selected from metal nitrates, metal chlorides, and metal sulfates. More preferably, the metal salt is a metal nitrate.

[0015] Preferably, the solvent of the metal salt solution includes water.

[0016] Preferably, the mass concentration of the metal salt solution is 0.05~0.5 mol / L; more preferably, the mass concentration of the metal salt solution is 0.1~0.4 mol / L; even more preferably, the mass concentration of the metal salt solution is 0.15~0.35 mol / L; and even more preferably, the mass concentration of the metal salt solution is 0.18~0.25 mol / L.

[0017] Preferably, the mass-to-volume ratio of the MOF to the metal salt solution is 1 g: (50~600) mL; more preferably, the mass-to-volume ratio of the MOF to the metal salt solution is 1 g: (70~560) mL; even more preferably, the mass-to-volume ratio of the MOF to the metal salt solution is 1 g: (80~520) mL; and even more preferably, the mass-to-volume ratio of the MOF to the metal salt solution is 1 g: (100~500) mL.

[0018] Preferably, before high-temperature activation in step S1, the metal salt solution containing the MOF is first subjected to ultrasonic treatment. Ultrasonic treatment allows the MOF to be fully immersed in the metal salt solution.

[0019] Preferably, the ultrasound duration is 20-50 minutes; more preferably, the ultrasound duration is 22-45 minutes; even more preferably, the ultrasound duration is 22-40 minutes; and even more preferably, the ultrasound duration is 26-35 minutes.

[0020] Preferably, the high-temperature activation temperature in step S1 is 180~260℃; more preferably, the high-temperature activation temperature in step S1 is 190~255℃; and even more preferably, the high-temperature activation temperature in step S1 is 200~250℃.

[0021] Preferably, the high-temperature activation time in step S1 is 1.5~5h; more preferably, the high-temperature activation time in step S1 is 1.6~4.5h; even more preferably, the high-temperature activation time in step S1 is 1.8~4.2h; and even more preferably, the high-temperature activation time in step S1 is 1.9~3h.

[0022] Preferably, the method for separating the solid phase in step S1 includes centrifugation followed by drying. More preferably, the product after centrifugation is washed before drying.

[0023] Preferably, the drying temperature is 50~90℃; more preferably, the drying temperature is 52~88℃; and even more preferably, the drying temperature is 60~80℃.

[0024] Preferably, the drying time is 10-16 hours; more preferably, the drying time is 11-15 hours; and even more preferably, the drying time is 12-14 hours.

[0025] Preferably, in step S2, the strength of the magnetic field is 0.5~5T; more preferably, in step S2, the strength of the magnetic field is 0.6~4T; even more preferably, in step S2, the strength of the magnetic field is 0.8~3T; and even more preferably, in step S2, the strength of the magnetic field is 1~2T.

[0026] Preferably, in step S2, the carbonization temperature is 500~1000℃; more preferably, in step S2, the carbonization temperature is 550~950℃; even more preferably, in step S2, the carbonization temperature is 580~920℃; and even more preferably, in step S2, the carbonization temperature is 600~900℃.

[0027] Preferably, the carbonization time is 0.5-5 hours; more preferably, the carbonization time is 0.6-4 hours; even more preferably, the carbonization time is 0.8-3.5 hours; and even more preferably, the carbonization time is 1-3 hours.

[0028] Preferably, after carbonization is completed, the magnetic field is maintained until the temperature drops below 200°C, at which point the magnetic field is turned off.

[0029] To achieve the second objective mentioned above, the present invention provides the following technical solution.

[0030] Secondly, the present invention provides a porous carbon material loaded with metal nanoparticles, which is prepared by the preparation method described in the first aspect.

[0031] The porous carbon material supported on metal nanoparticles provided by this invention has a regular structure with numerous internal pores and no collapse or aggregation. The supported metal nanoparticles are orderly dispersed and extremely small in size, oriented and assembled within the porous carbon structure to form highly uniform bimetallic active centers. The porous carbon material supported on metal nanoparticles of this invention exhibits strong structural stability, which is beneficial for immobilizing and loading active substances such as sulfur and for the efficient catalysis of polysulfides.

[0032] To achieve the third objective mentioned above, the present invention provides the following technical solution.

[0033] Thirdly, the present invention provides a battery cathode material, the battery cathode material comprising the porous carbon material loaded with metal nanoparticles as described in the second aspect and elemental sulfur.

[0034] Preferably, the mass ratio of the porous carbon material loaded with metal nanoparticles to elemental sulfur is 1:(4~6); more preferably, the mass ratio of the porous carbon material loaded with metal nanoparticles to elemental sulfur is 1:(4.2~5.8); and even more preferably, the mass ratio of the porous carbon material loaded with metal nanoparticles to elemental sulfur is 1:(4.5~5.5).

[0035] Preferably, the battery cathode material is prepared by the following method: mixing the porous carbon material loaded with metal nanoparticles as described in the second aspect with elemental sulfur and then heating it to obtain the battery cathode material.

[0036] Preferably, the heating temperature is 140~170℃; more preferably, the heating temperature is 145~165℃; and even more preferably, the heating temperature is 150~160℃.

[0037] Preferably, the heating time is 10-16 hours; more preferably, the heating time is 11-14 hours; and even more preferably, the heating time is 11.5-13 hours.

[0038] Fourthly, the present invention provides a lithium-sulfur battery, wherein the positive electrode of the lithium-sulfur battery comprises the battery positive electrode material described in the third aspect.

[0039] Preferably, the initial capacity of the lithium-sulfur battery is ≥1300mAh g. -1 More preferably, the initial capacity of the lithium-sulfur battery is ≥1310 mAh g. -1 More preferably, the initial capacity of the lithium-sulfur battery is ≥1315 mAh g. -1 More preferably, the initial capacity of the lithium-sulfur battery is 1316~1325 mAh g. -1 .

[0040] Preferably, the lithium-sulfur battery retains ≥75% capacity after 2000 cycles at a current density of 5C; more preferably, the lithium-sulfur battery retains ≥76% capacity after 2000 cycles at a current density of 5C.

[0041] Fifthly, the present invention provides the application of the porous carbon material loaded with metal nanoparticles as described in the second aspect, the battery cathode material as described in the third aspect, and the lithium-sulfur battery as described in the fourth aspect in portable electronic devices, electric vehicles, drones, or energy storage systems.

[0042] The beneficial effects of this invention are: (1) In this invention, metal ions from a metal salt solution are adsorbed within the porous structure of a MOF. High-temperature activation enables the metal ions to be efficiently and uniformly dispersed within the pores of the MOF, achieving atomic-level metal ion doping in the resulting metal-MOF precursor. Then, carbonization in a magnetic field reduces the uniformly distributed metal ions in the metal-MOF precursor to metal nanoparticles, simultaneously achieving ordered dispersion of the metal nanoparticles. The organic portion of the metal-MOF precursor is carbonized to form a porous carbon material, thus yielding a porous carbon material loaded with metal nanoparticles. The synergistic effect of high-temperature activation and magnetic field carbonization in this invention achieves precise cross-scale control from atomic-level doping to nanoscale directional assembly, preparing a porous carbon material loaded with metal nanoparticles that possesses both high-density active sites and excellent conductivity.

[0043] (2) The porous carbon material loaded with metal nanoparticles provided by this invention has a regular structure with numerous internal pores, and the porous carbon framework does not collapse. The loaded nanoparticles are extremely small in size, exhibit no aggregation, and have good structural stability. The loaded metal nanoparticles are orderly dispersed and extremely small in size, and they are oriented and assembled within the porous carbon structure, forming highly uniform bimetallic active centers. The porous carbon material loaded with metal nanoparticles of this invention has strong structural stability, which helps to fix and load active substances such as sulfur and catalyze polysulfides.

[0044] (3) The lithium-sulfur battery provided by the present invention has excellent initial capacity and cycle stability, with an initial capacity as high as 1319 mAh g.-1 After 2000 cycles at a current density of 5C, the capacity retention rate is still greater than 75%, making it suitable for applications in portable electronic devices, electric vehicles, drones, or energy storage systems. Attached Figure Description

[0045] Figure 1 Transmission electron microscopy images of CoFe@NC-1 and CoFe@NC-1 (compare 1); Figure 2 High-resolution TEM image of CoFe@NC-1; Figure 3 The performance curves of the lithium-sulfur battery of Example 4 and the lithium-sulfur battery of Comparative Example 2 after 100 cycles at 5C are shown. Figure 4 The performance curve of the lithium-sulfur battery in Example 4 after 2000 cycles at 5C is shown. Detailed Implementation

[0046] To enable those skilled in the art to better understand this application, the present invention will be further described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims.

[0047] The materials used in this invention are as follows: Lithium-sulfur electrolyte, brand: Duoduo Chemical, item number: LS-042.

[0048] In the description of this invention, it should be noted that unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Furthermore, to better illustrate this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this invention can be practiced even without certain specific details. In some embodiments, raw materials, methods, and means well known to those skilled in the art are not described in detail in order to highlight the main points of this invention.

[0049] Example 1 This embodiment provides a porous carbon material loaded with cobalt-iron metal nanoparticles, and the preparation method is as follows: Step 1: Preparation of ZIF-67 Step 1.1: Disperse 10 mmol of cobalt nitrate hexahydrate in 200 mL of methanol as solution A; disperse 20 mmol of 2-methylimidazole in 250 mL of methanol as solution B; Step 1.2: While liquid A is being magnetically stirred, liquid B is poured into liquid A and stirred for 6 minutes until the mixture is homogeneous, thus obtaining the ZIF-67 precursor solution; Step 1.3: Seal the ZIF-67 precursor solution obtained in Step 1.2 and let it stand for 24 hours to age, thus obtaining the ZIF-67 solution; Step 1.4: After centrifuging the ZIF-67 solution obtained in Step 1.3, take the precipitate, wash the precipitate three times with methanol and ethanol respectively, and then dry it overnight at 60℃ to obtain ZIF-67 powder.

[0050] Step 2: Synthesize and activate iron-doped ZIF-67 (Fe 3+ / ZIF-67) precursor Step 2.1: Take 0.2g of ZIF-67 powder prepared in Step 1 and disperse it in 50mL of 0.2mol / L ferric nitrate aqueous solution, and sonicate for 30min to obtain a mixed solution; Step 2.2: Transfer the mixed solution from Step 2.1 to a high-pressure reactor, seal it, and place it in a tube furnace. Under the protection of inert argon gas, heat it to 200°C at a heating rate of 2°C / min and hold it at this temperature for 2 hours to complete the high-temperature liquid-phase activation process. After the reactor cools naturally to room temperature, collect the product by centrifugation, wash it three times with ethanol, and vacuum dry it at 60°C for 12 hours to obtain activated Fe. 3+ / ZIF-67 precursor.

[0051] Step 3: Induced carbonization in a magnetic field Step 3.1: Take the Fe obtained in step 2 3+ / ZIF-67 precursor powder is evenly spread in a ceramic boat and placed in the center of the constant temperature heating zone of a tube furnace. A pair of electromagnets are placed parallel to each other on both sides of the tube furnace to generate a uniform external magnetic field with an intensity of 1T. Step 3.2: Under the condition of continuously applying the external magnetic field of Step 3.1, inert gas is introduced into the tube furnace, and the temperature is programmed to rise to 600℃ at a rate of 2℃ / min, and carbonized at this temperature for 3 hours. Step 3.3: After the carbonization reaction is completed, maintain the magnetic field until the furnace temperature drops below 200°C, then turn off the magnetic field and continue cooling to room temperature to obtain a porous carbon material loaded with cobalt-iron metal nanoparticles (denoted as CoFe@NC-1).

[0052] Example 2 This embodiment provides a porous carbon material loaded with cobalt-iron metal nanoparticles, and the preparation method is as follows: Step 1: Preparation of ZIF-67 Step 1.1: Disperse 15 mmol of cobalt nitrate hexahydrate in 250 mL of methanol as solution A; disperse 30 mmol of 2-methylimidazole in 250 mL of methanol as solution B; Step 1.2: While liquid A is being magnetically stirred, liquid B is poured into liquid A and stirred for 8 minutes until uniformly mixed to obtain ZIF-67 precursor solution; Step 1.3: Seal the ZIF-67 precursor solution obtained in Step 1.2 and let it stand for 24 hours to age, thus obtaining the ZIF-67 solution; Step 1.4: After centrifuging the ZIF-67 solution obtained in Step 1.3, take the precipitate, wash the precipitate three times with methanol and ethanol respectively, and then dry it overnight at 70℃ to obtain ZIF-67 powder.

[0053] Step 2: Synthesize and activate iron-doped ZIF-67 (Fe 3+ / ZIF-67) precursor Step 2.1: Take 0.3g of ZIF-67 powder prepared in Step 1 and disperse it in 70mL of 0.2mol / L ferric nitrate aqueous solution, and sonicate for 30min to obtain a mixed solution; Step 2.2: Transfer the mixed solution from Step 2.1 to a high-pressure reactor, seal it, and place it in a tube furnace. Under the protection of inert argon gas, heat it to 220°C at a heating rate of 3°C / min and hold it at this temperature for 3 hours to complete the high-temperature liquid-phase activation process. After the reactor cools naturally to room temperature, collect the product by centrifugation, wash it three times with ethanol, and vacuum dry it at 70°C for 12 hours to obtain activated Fe. 3+ / ZIF-67 precursor.

[0054] Step 3: Induced carbonization in a magnetic field Step 3.1: Take the Fe obtained in step 2 3+ / ZIF-67 precursor powder is evenly spread in a ceramic boat and placed in the center of the constant temperature heating zone of a tube furnace. A pair of electromagnets are placed parallel to each other on both sides of the tube furnace to generate a uniform external magnetic field with an intensity of 1.5T. Step 3.2: Under the condition of continuously applying the external magnetic field of Step 3.1, inert gas is introduced into the tube furnace, and the temperature is programmed to rise to 700℃ at a rate of 2℃ / min, and carbonized at this temperature for 2 hours. Step 3.3: After the carbonization reaction is completed, maintain the magnetic field until the furnace temperature drops below 200℃, then turn off the magnetic field and continue cooling to room temperature to obtain a porous carbon material loaded with cobalt-iron metal nanoparticles (denoted as CoFe@NC-2).

[0055] Example 3 This embodiment provides a porous carbon material loaded with cobalt-iron metal nanoparticles, and the preparation method is as follows: Step 1: Preparation of ZIF-67 Step 1.1: Disperse 20 mmol of cobalt nitrate hexahydrate in 300 mL of methanol as solution A; disperse 40 mmol of 2-methylimidazole in 300 mL of methanol as solution B; Step 1.2: While liquid A is being magnetically stirred, liquid B is poured into liquid A and stirred for 10 minutes until homogeneous to obtain ZIF-67 precursor solution; Step 1.3: Seal the ZIF-67 precursor solution obtained in Step 1.2 and let it stand for 24 hours to age, thus obtaining the ZIF-67 solution; Step 1.4: After centrifuging the ZIF-67 solution obtained in Step 1.3, take the precipitate, wash the precipitate three times with methanol and ethanol respectively, and then dry it overnight at 80℃ to obtain ZIF-67 powder.

[0056] Step 2: Synthesize and activate iron-doped ZIF-67 (Fe 3+ / ZIF-67) precursor Step 2.1: Take 0.5g of ZIF-67 powder prepared in Step 1 and disperse it in 100mL of 0.2 mol / L ferric nitrate aqueous solution, and sonicate for 30min to obtain a mixed solution; Step 2.2: Transfer the mixed solution from Step 2.1 to a high-pressure reactor, seal it, and place it in a tube furnace. Under the protection of inert argon gas, heat it to 250°C at a heating rate of 5°C / min and hold it at this temperature for 2 hours to complete the high-temperature liquid-phase activation process. After the reactor cools naturally to room temperature, collect the product by centrifugation, wash it three times with ethanol, and vacuum dry it at 80°C for 12 hours to obtain activated Fe. 3+ / ZIF-67 precursor.

[0057] Step 3: Induced carbonization in a magnetic field Step 3.1: Take the Fe obtained in step 2 3+ / ZIF-67 precursor powder is evenly spread in a ceramic boat and placed in the center of the constant temperature heating zone of a tube furnace. A pair of electromagnets are placed parallel to each other on both sides of the tube furnace to generate a uniform external magnetic field with an intensity of 2T. Step 3.2: Under the condition of continuously applying the external magnetic field of Step 3.1, inert gas is introduced into the tube furnace, and the temperature is programmed to rise to 900℃ at a rate of 5℃ / min, and carbonized at this temperature for 1 hour. Step 3.3: After the carbonization reaction is completed, maintain the magnetic field until the furnace temperature drops below 200°C, then turn off the magnetic field and continue cooling to room temperature to obtain a porous carbon material loaded with cobalt-iron metal nanoparticles (denoted as CoFe@NC-3).

[0058] Example 4 This embodiment provides a lithium-sulfur battery, which is prepared using the following method: Step 1: Mix CoFe@NC-1 prepared in Example 1 and elemental sulfur at a mass ratio of 1:5. Heat at 155°C for 12 hours under an inert atmosphere to allow sulfur to melt and diffuse into the pores of CoFe@NC-1, thus obtaining the battery cathode material, denoted as S / CoFe@NC-1. Step 2: Using S / CoFe@NC-1 as the positive electrode, lithium metal as the counter electrode and reference electrode, porous polypropylene as the separator, and lithium-sulfur electrolyte, CR2025 coin cells are assembled in an argon-filled glove box.

[0059] Example 5 This embodiment provides a lithium-sulfur battery, which is prepared using the following method: Step 1: Mix CoFe@NC-2 prepared in Example 2 and elemental sulfur at a mass ratio of 1:5. Heat at 155°C for 12 hours under an inert atmosphere to allow sulfur to melt and diffuse into the pores of CoFe@NC-2, thus obtaining the battery cathode material, denoted as S / CoFe@NC-2. Step 2: Using S / CoFe@NC-2 as the positive electrode, lithium metal as the counter electrode and reference electrode, porous polypropylene as the separator, and lithium-sulfur electrolyte, CR2025 coin cells are assembled in an argon-filled glove box.

[0060] Example 6 This embodiment provides a lithium-sulfur battery, which is prepared using the following method: Step 1: Mix CoFe@NC-3 prepared in Example 3 and elemental sulfur at a mass ratio of 1:5. Heat at 155°C for 12 hours under an inert atmosphere to allow sulfur to melt and diffuse into the pores of CoFe@NC-3, thus obtaining the battery cathode material, denoted as S / CoFe@NC-3. Step 2: Using S / CoFe@NC-3 as the positive electrode, lithium metal as the counter electrode and reference electrode, porous polypropylene as the separator, and lithium-sulfur electrolyte, CR2025 coin cells are assembled in an argon-filled glove box.

[0061] Comparative Example 1 This comparative example provides a porous carbon material loaded with cobalt-iron metal nanoparticles. The difference between this and Example 1 is that no magnetic field is used in this comparative example; that is, step 3 only involves loading Fe... 3+ The ZIF-67 precursor powder was carbonized in a tube furnace at 600°C for 3 hours. All other steps were the same as in Example 1. The resulting material was denoted as CoFe@NC-Comparative 1.

[0062] Comparative Example 2 This comparative example provides a lithium-sulfur battery, which is prepared using the following method: Step 1: Mix CoFe@NC-Comparative 1 prepared in Comparative Example 1 and elemental sulfur at a mass ratio of 1:5. Heat at 155°C for 12 hours under an inert atmosphere to allow sulfur to melt and diffuse into the channels of CoFe@NC-Comparative 1, thereby obtaining the battery cathode material, denoted as S / CoFe@NC-Comparative 1. Step 2: Using S / CoFe@NC-Comparison 1 as the positive electrode, lithium metal as the counter electrode and reference electrode, porous polypropylene as the separator, and lithium-sulfur electrolyte, CR2025 coin cells are assembled in an argon-filled glove box.

[0063] Morphological characteristics CoFe@NC-1, CoFe@NC-2 and CoFe@NC-3 have similar morphology and properties. This invention uses CoFe@NC-1 as an example for characterization and illustration.

[0064] Figure 1 Transmission electron microscopy images of CoFe@NC-1 and CoFe@NC-1 (compare 1). Figure 1 In the table, a represents CoFe@NC-1, and b represents CoFe@NC-1 (comparison 1). Figure 1 It can be seen that CoFe@NC-1 has a regular structure with many internal pores, and the porous carbon framework does not collapse; the nanoparticles it supports are extremely small in size, without agglomeration, and have good structural stability. In contrast, CoFe@NC-1 prepared by direct carbonization without magnetic field induction has fewer internal pores, uneven distribution of nanoparticles, obvious agglomeration, and poor structural stability. Figure 1 This indicates that magnetic field-induced carbonization can cause the loaded metal nanoparticles to disperse in an orderly manner, achieving atomic-level loading of iron and cobalt, and directional arrangement and assembly in the porous carbon framework structure, which is beneficial for the loading of sulfur in porous carbon materials.

[0065] Figure 2 High-resolution TEM (HRTEM) image of CoFe@NC-1. (Source: [Original Source Name]) Figure 2 It can be seen that the lattice of metallic Fe and Co can be clearly seen in CoFe@NC-1 and they are uniformly dispersed, indicating that CoFe@NC-1 forms a highly uniform bimetallic active center with a high density of active sites, which can help fix the active substance sulfur and catalyze polysulfides, and suppress the "shuttle effect".

[0066] Performance testing The lithium-sulfur batteries in Examples 4-6 have similar battery performance. This invention uses the lithium-sulfur battery prepared in Example 4 as an example for testing and explanation.

[0067] The lithium-sulfur battery of Example 4 and the lithium-sulfur battery of Comparative Example 2 were cycled 100 times at a current density of 5C to test their cycle stability. The test results are as follows: Figure 3 As shown. Figure 3The performance curves of the lithium-sulfur battery of Example 4 and the lithium-sulfur battery of Comparative Example 2 after 100 cycles at 5C are shown. Figure 3 The black line represents the lithium-sulfur battery of Example 4, and the red line represents the lithium-sulfur battery of Comparative Example 2. Figure 3 It can be seen that the initial capacity of the lithium-sulfur battery in Example 4 is 1319 mAh g. -1 The initial capacity of the lithium-sulfur battery in Comparative Example 2 was 1206 mAh g. -1 After 100 cycles, the specific capacity of the lithium-sulfur battery in Example 4 was 1169 mAhg. -1 The specific capacity of the lithium-sulfur battery in Comparative Example 2 was 976 mAh g. -1 . Figure 3 The results show that, compared with CoFe@NC-1, the lithium-sulfur battery prepared using CoFe@NC-1 (the cathode material formed by carbonization induced in a magnetic field) has better initial capacity and cycle stability. This indicates that the introduction of a magnetic field during the carbonization process can significantly improve the performance of the cathode material by enabling the loaded metal nanoparticles to be nano-sized and orderly dispersed, thereby improving the battery performance.

[0068] To further illustrate the excellent long-cycle performance of the lithium-sulfur battery in Example 4, the lithium-sulfur battery in Example 4 was cycled 2000 times at a current density of 5C to test its long-cycle stability. The test results are as follows: Figure 4 As shown. Figure 4 The performance curve of the lithium-sulfur battery in Example 4 after 2000 cycles at 5C is shown. Figure 4 It can be seen that after 2000 long cycles, the specific capacity of the lithium-sulfur battery is still 1003 mAh g. -1 The capacity retention rate is approximately 76% (1003 / 1319). Figure 4 This indicates that the bimetallic sites of CoFe@NC-1 have a strong confinement effect on sulfur, and its catalytic activity for polysulfides significantly improves the reaction kinetics of lithium-sulfur batteries, thereby enhancing the cycle stability and lifespan of lithium-sulfur batteries.

[0069] In summary, this invention adsorbs metal ions from a metal salt solution within the porous structure of a MOF (Metal-Oxide-Foil Composite). High-temperature activation efficiently and uniformly disperses these metal ions within the pores of the MOF, achieving atomic-level metal ion doping in the resulting metal-MOF precursor. Then, carbonization in a magnetic field reduces the uniformly distributed metal ions in the precursor to metal nanoparticles, simultaneously achieving ordered dispersion of the nanoparticles. The organic components in the precursor are also carbonized to form a porous carbon material, resulting in a porous carbon material loaded with metal nanoparticles. The synergistic effect of high-temperature activation and magnetic field carbonization in this invention enables precise cross-scale control from atomic-level doping to nanoscale directional assembly, producing a porous carbon material loaded with metal nanoparticles that possesses both high-density active sites and excellent conductivity.

[0070] The porous carbon material with metal nanoparticles prepared in this invention has a regular structure with numerous internal pores. The porous carbon framework does not collapse, and the supported nanoparticles are extremely small in size, exhibiting no aggregation and good structural stability. The supported metal nanoparticles are orderly dispersed and extremely small in size, oriented and assembled within the porous carbon structure, forming highly uniform bimetallic active centers. Its strong structural stability facilitates the fixation and loading of active sulfur and the catalysis of polysulfides. The lithium-sulfur battery prepared using CoFe@NC-1 as the cathode material in this invention exhibits excellent initial capacity and cycle stability, with an initial capacity as high as 1319 mAh g⁻¹. -1 After 2000 cycles at a current density of 5C, the capacity retention rate is still greater than 75%, making it suitable for applications in portable electronic devices, electric vehicles, drones, or energy storage systems. In contrast, porous carbon materials obtained through direct carbonization without magnetic field induction exhibit agglomeration of metal nanoparticles, limiting their effectiveness in improving battery performance.

[0071] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing porous carbon materials loaded with metal nanoparticles, characterized in that, Includes the following steps: S1: Disperse MOF in a metal salt solution, then activate it at high temperature, and separate the solid phase after activation to obtain a metal ion-doped MOF precursor; the metal salt includes at least one of iron salt and nickel salt; the high temperature activation temperature is 180~260℃; S2: Carbonize the metal ion-doped MOF precursor described in step S1 in a magnetic field to obtain the porous carbon material loaded with metal nanoparticles.

2. The method for preparing porous carbon materials loaded with metal nanoparticles according to claim 1, characterized in that, The MOF mentioned in step S1 includes ZIF-67.

3. The method for preparing porous carbon materials loaded with metal nanoparticles according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of the MOF to the metal salt solution is 1 g: (50~600) mL.

4. The method for preparing porous carbon materials loaded with metal nanoparticles according to claim 1, characterized in that, The high-temperature activation time in step S1 is 1.2~5h.

5. The method for preparing porous carbon materials loaded with metal nanoparticles according to claim 1, characterized in that, The strength of the magnetic field in step S2 is 0.5~5T.

6. The method for preparing porous carbon materials loaded with metal nanoparticles according to claim 1, characterized in that, The carbonization temperature in step S2 is 500~1000℃; And / or, the carbonization time is 0.5~5h.

7. A porous carbon material loaded with metal nanoparticles, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. A battery positive electrode material, characterized in that, The positive electrode material of the battery includes the porous carbon material with loaded metal nanoparticles as described in claim 7 and elemental sulfur.

9. A lithium-sulfur battery, characterized in that, The positive electrode of the lithium-sulfur battery comprises the battery positive electrode material as described in claim 8.

10. The application of the porous carbon material loaded with metal nanoparticles as described in claim 7, the battery cathode material as described in claim 8, or the lithium-sulfur battery as described in claim 9 in portable electronic devices, electric vehicles, drones, or energy storage systems.

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