Preparation method of monatomic modified porous carbon material and application thereof in lithium-sulfur battery

Abstract

The application discloses a preparation method of single-atom modified porous carbon material and application of the single-atom modified porous carbon material in lithium-sulfur batteries. The preparation method comprises the following steps: preparing zinc-based metal organic framework material Zn-MOF nanoparticles; coating phenolic resin (RF) on surfaces of the Zn-MOF nanoparticles to obtain Zn-MOF-RF nanoparticles; adsorbing X metal salt on the Zn-MOF-RF nanoparticles by using a solution immersion method; and obtaining X single-atom loaded hollow nitrogen-doped porous carbon (X-N / HNPC) composite material by high-temperature carbonization under an inert atmosphere. The composite material has a large specific surface area and rich pore size structure, and as a positive electrode material, can not only improve the utilization rate of active material sulfur, but also effectively adsorb polysulfides by high catalytic active sites, improve redox reaction kinetics, and further inhibit the shuttle effect of polysulfides. Based on the lithiumophilicity of metal single atoms, as a lithium negative electrode carrier, the lithium uniform deposition can be regulated, the growth of lithium dendrites can be relieved, and the stability of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery materials technology, specifically to a method for preparing a single-atom modified porous carbon material and its application in lithium-sulfur batteries. Background Technology

[0002] The development of new energy fields has driven progress in energy storage, increasing societal demand for energy storage systems. However, current commercial lithium-ion battery development is limited by the materials used in positive and negative electrodes, and its energy density is approaching its theoretical limit, making it difficult to meet societal needs. Therefore, it is necessary to develop new energy storage systems to support the development of green energy technologies. Lithium-sulfur batteries are considered one of the most promising new electrochemical energy storage technologies due to their high theoretical energy density (2500 Wh / kg), abundant sulfur resources, low cost, and minimal environmental pollution. However, lithium-sulfur batteries still face some challenges. Regarding the positive electrode, the inherent insulating properties of the active material sulfur and the discharge product lithium sulfide result in low conductivity of the positive electrode material, affecting the electrochemical reaction rate. The density difference between sulfur and lithium sulfide leads to volume expansion of the positive electrode material during charging and discharging, causing electrode shedding. The intermediate polysulfides generated during redox reactions dissolve in the electrolyte and, under the influence of the concentration gradient, shuttle to the negative electrode to react directly with lithium, causing irreversible loss of active materials and severely impacting battery performance. The slow reaction kinetics of polysulfides also limit the battery's capacity. On the negative electrode side, the uneven surface and uneven current density distribution of the lithium negative electrode lead to uneven lithium deposition, forming lithium dendrites that continue to grow during the deposition process. These dendrites may puncture the separator, affecting battery safety. Therefore, solving these problems is key to the commercialization of lithium-sulfur batteries.

[0003] Developing and designing multifunctional composite cathode materials and protecting lithium anodes are key to solving the aforementioned problems. Currently, porous carbon materials are commonly used as sulfur supports to improve the conductivity of cathode materials. Porous carbon materials also possess a large specific surface area, providing more sulfur loading sites and improving the utilization rate of sulfur, the active material. Furthermore, the abundant pore structure provides three-dimensional ion transport channels and alleviates the volume expansion of the cathode material during charge and discharge, effectively improving the cycle stability of lithium-sulfur batteries. However, non-polar carbon materials have a weak effect on polysulfides and cannot effectively adsorb and catalyze their conversion. Therefore, in recent years, a series of electrocatalytic materials have been applied to the design of lithium-sulfur battery cathode materials, such as metal nitrides, metal oxides, metal sulfides, and metal carbides. However, since the catalytic conversion reactions of these catalysts all occur on the catalyst surface, the catalytic active sites cannot be fully utilized. Therefore, developing catalytic materials with high atom utilization and strong catalytic activity for application in lithium-sulfur batteries is of great significance. In addition, the protection of lithium anodes is also particularly important. The uncontrollable growth of lithium dendrites is mainly due to the uneven deposition of lithium ions. Studies have shown that it is feasible to regulate the deposition of lithium ions by developing lithiophilic materials as carriers for lithium anodes.

[0004] The purpose of this invention is to design a multifunctional, highly active catalytic material that can physically confine lithium polysulfides, chemically adsorb and catalytically convert them, and regulate lithium-ion deposition, so as to improve the discharge capacity, cycle stability and rate performance of lithium-sulfur batteries. Summary of the Invention

[0005] To address the aforementioned problems in lithium-sulfur batteries, this invention provides a method for preparing a single-atom modified porous carbon material and its application in lithium-sulfur batteries. When this composite material is used in lithium-sulfur batteries, its hollow porous structure can physically confine and chemically adsorb polysulfides. The numerous highly catalytically active sites can improve the conversion reaction kinetics of polysulfides, significantly enhancing the discharge specific capacity, cycle performance, and rate performance of lithium-sulfur batteries.

[0006] The technical problem of this invention is solved by adopting the following technical solution: A method for preparing a highly catalytically active composite material includes the following steps: (1) Preparation of zinc-based metal-organic framework (Zn-MOF) particles; (2) Coating Zn-MOF particles with phenolic resin (RF) yields Zn-MOF-RF particles; (3) The metal salt X is uniformly loaded onto Zn-MOF-RF particles by solution impregnation; (4) The material obtained in step (3) is carbonized at high temperature in an inert gas atmosphere to obtain a hollow porous carbon material (XN / HNPC) modified with a highly catalytically active X single-atom catalyst.

[0007] Furthermore, in step (1), the metal-organic framework material is a zinc-based metal-organic framework material composed of zinc metal ions, 2-methylimidazole (C4H6N2), and hexadecyltrimethylammonium bromide (CTAB). The preparation methods of the zinc-based metal-organic framework material can be commonly used methods such as hydrothermal / solvothermal synthesis, ultrasonic method, microwave heating method, electrochemical method, and mechanochemical synthesis method.

[0008] Preferably, the zinc-based metal-organic framework material prepared in step (1) has a cubic structure with a particle size of 30 nm to 2 μm, possesses abundant pore structures such as micropores and mesopores, and has a specific surface area greater than 300 m². 2 / g.

[0009] The zinc-based metal-organic framework material prepared in step (1) contains nitrogen.

[0010] Preferably, in step (1), cubic Zn-MOF nanoparticles are obtained by introducing hexadecyltrimethylammonium bromide into the solvent, wherein the mass ratio of CTAB to zinc nitrate is 1:100 to 2:100.

[0011] The phenolic resin-formaldehyde coating in step (2) is performed by epitaxial growth in a solvent onto the Zn-MOF particles prepared in step (1). Specifically, the phenolic resin (RF) coating in step (2) involves uniformly dispersing Zn-MOF nanoparticles in a mixed solution of resorcinol and formaldehyde, magnetically stirring at room temperature for 18-24 hours, collecting the precipitate by centrifugation or filtration, washing with deionized water and ethanol, and drying in a vacuum oven at 60 °C for 6-12 hours. The mass ratio of resorcinol to formaldehyde in the mixed solution is 1:150, and the mass ratio of resorcinol to Zn-MOF nanoparticles is 5:100-10:100.

[0012] In step (3), the solution impregnation method involves uniformly dispersing the Zn-MOF-RF material in an X metal salt solution, magnetically stirring at room temperature for 12-24 hours, collecting the precipitate by centrifugation or filtration, washing it with deionized water and ethanol, and drying it in a vacuum oven at 60°C for 6-12 hours. The metal element X in the X metal salt solution is one or more transition metal elements, and the X metal salt includes acetate, nitrate, chlorate, chloride, etc. of the X metal. The concentration of metal ions in the X metal salt solution is 0.1-5 mg / mL, and the solution can be deionized water, ethanol, etc.

[0013] Preferably, the transition metal element is vanadium, nickel, cobalt, iron, manganese, etc.

[0014] Preferably, the mass ratio of the Zn-MOF-RF material to the metal ions is 100:0.5 to 100:2.

[0015] Furthermore, in step (4), the inert gas is nitrogen or argon, the high-temperature carbonization temperature is 900~1100 ℃ and the time is 2~5 hours. The zinc in Zn-MOF evaporates with the airflow at high temperature to obtain a porous carbon material XN / HNPC with uniform dispersion of X single atoms.

[0016] Preferably, the carbonization temperature is 900~1000 ℃ and the carbonization time is 3~5 hours.

[0017] This invention also provides structural information on a highly catalytically active single-atom modified XN / HNPC composite material prepared using the aforementioned method, wherein X single atoms are uniformly dispersed on the surface of a porous carbon material. The mass fraction of the carbon-based support material ranges from 98% to 99.9%; the metallic X exists in single-atom form, with a mass fraction ranging from 0.1% to 2%.

[0018] Preferably, the mass fraction of the metal single atom is 0.5% to 2%.

[0019] Preferably, the specific surface area of ​​the composite material is greater than 400 m². 2 / g, with a particle size of 200 nm to 2 μm, and rich pore structures including micropores and mesopores.

[0020] The present invention also provides a lithium-sulfur battery, wherein the positive and / or negative electrodes of the lithium-sulfur battery contain the aforementioned highly catalytically active single-atom modified XN / HNPC composite material.

[0021] Preferably, in a lithium-sulfur battery, the positive electrode is prepared by using a highly catalytically active single-atom-loaded XN / HNPC composite material as the positive electrode sulfur-carrying material, and the negative electrode is a copper foil modified with a pre-lithium-plated XN / HNPC composite material. The electrolyte is composed of lithium salt, non-aqueous organic solvent and lithium nitrate. The electrolyte is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a concentration of 1 mol / L. The non-aqueous organic solvent is a mixture of dioxolane (DOL) and dimethyl ethylene glycol (DME) in a volume ratio of 1:1. Lithium nitrate is added at 1% of the total electrolyte mass.

[0022] This invention also provides an application of a porous carbon material modified with a single-atom catalyst in a lithium-sulfur battery, using the XN / HNPC composite material as a positive electrode sulfur carrier and / or a negative electrode lithium support.

[0023] (I) The porous carbon material XN / HNPC modified with the above-mentioned single-atom catalyst is used as the positive electrode sulfur support material for lithium-sulfur batteries. The specific steps are as follows: (a) Sublimed sulfur and XN / HNPC composite material are uniformly mixed according to the corresponding mass ratio. Under vacuum or inert gas (nitrogen or argon) conditions, sulfur / XN / HNPC composite cathode material is obtained by melt diffusion method. The melting heating temperature is 155 °C and the holding time is 12~18 hours. The mass ratio of XN / HNPC in the composite cathode material is 10%~50%.

[0024] Preferably, sulfur loading is carried out under vacuum, and the mass ratio of XN / HNPC material in the resulting composite cathode material is 20%~40%.

[0025] (b) The sulfur / carbon composite cathode material obtained in step (a) is uniformly mixed with a conductive agent and a binder in a certain proportion. Using nitrogen-methylpyrrolidone (NMP) as a solvent, the mixture is uniformly mixed to form a slurry, which is then coated onto a current collector. After vacuum drying, a lithium-sulfur battery cathode sheet is prepared.

[0026] Preferably, the mass ratio of sulfur / carbon composite cathode material, conductive agent and binder is (80-90):(5-10):(5-10).

[0027] The conductive agent is one or more of conductive carbon black, conductive graphite, carbon nanotubes, and graphene, and the binder is polyvinylidene fluoride.

[0028] Preferably, the homogenization method for preparing the slurry is ball milling, with a milling time of 1-2 hours, and the sulfur loading of the lithium-sulfur battery positive electrode sheet is 0.5-5 mg / cm³. 2 .

[0029] Preferably, the positive electrode current collector used is carbon-coated aluminum foil.

[0030] (c) Assemble the positive electrode, lithium sheet, separator, electrolyte and shell obtained in step (b) to obtain a lithium-sulfur battery and perform electrochemical testing.

[0031] (II) The porous carbon material XN / HNPC composite material modified with the above-mentioned single-atom catalyst is used as the lithium anode support material. The specific steps are as follows: (a) The XN / HNPC composite material is mixed with a conductive agent and a binder in a certain proportion, and N-methylpyrrolidone is used as a solvent. After being mixed evenly, the mixture is coated on the surface of a copper foil and then dried under vacuum to obtain a copper foil loaded with the XN / HNPC composite material.

[0032] Preferably, the mass ratio of XN / HNPC composite material, conductive agent and binder is (80-90):(5-10):(5-10).

[0033] Preferably, the loading of the XN / HNPC composite material on the copper foil surface is 0.5~0.8 mg / cm². 2 .

[0034] (b) Using the XN / HNPC composite material-modified copper foil obtained in step (a) as the electrode and the lithium sheet as the counter electrode, the battery is assembled with the electrolyte and casing. Negative electrode preparation: The current density for the first three cycles is 0.2 mA / cm². 2 Activation was performed by charge-discharge cycle between 0 and 1 V, followed by a cycle of 0.2 mA / cm². 2 The current density was used to pre-plate Li onto XN / HNPC, with a lithium content of 15 mAh / cm³. 2 The pre-lithium-plated electrode is removed and used as the negative electrode.

[0035] (c) The pre-plated lithium electrode is removed and used as the negative electrode. The positive electrode, separator and electrolyte are assembled using commercially available carbon nanotubes as sulfur carrier materials to obtain a lithium-sulfur battery.

[0036] (III) The above-mentioned single-atom modified porous carbon material XN / HNPC is used as the positive electrode sulfur carrier material and also as the negative electrode support material for lithium negative electrode protection. The specific steps are as follows: (1) Sublimed sulfur and XN / HNPC composite material are uniformly mixed in a certain proportion, and sulfur / carbon composite cathode material is obtained by melt-filling sulfur under vacuum or inert gas atmosphere. The heating temperature is 155 ℃ and the holding time is 12~18 hours. The mass ratio of single-atom modified porous carbon material XN / HNPC in sulfur / carbon composite cathode material is 20%~50%. (2) The sulfur / carbon composite cathode material, conductive agent and binder obtained in step 1) are mixed in a certain proportion. Using N-methylpyrrolidone as solvent, the mixture is mixed evenly to form a slurry and then evenly coated on the current collector. After vacuum drying, the positive electrode sheet of lithium-sulfur battery is obtained. The preparation of the positive electrode sheet is the same as the preparation method of the positive electrode sheet in (I). (3) The XN / HNPC composite material is mixed with a conductive agent and a binder in a certain proportion. Using N-methylpyrrolidone as a solvent, the mixture is thoroughly mixed to form a slurry, which is then coated onto a copper foil. After vacuum drying, the XN / HNPC composite material-modified copper foil is obtained as the electrode, and a lithium sheet is used as the counter electrode. A certain capacity of lithium is deposited on the surface of the XN / HNPC composite material-modified copper foil to obtain the modified lithium anode. Specifically, the anode preparation involves a current density of 0.2 mA / cm² for the first three turns. 2Activation was performed by charge-discharge cycle between 0 and 1V, followed by a cycle of 0.2 mA / cm². 2 The current density was used to pre-plate Li onto XN / HNPC, with a lithium content of 15 mAh / cm³. 2 The pre-plated lithium electrode is removed and used as the negative electrode; the preparation of the lithium negative electrode is the same as the preparation method of the lithium negative electrode in (II); (4) The lithium-sulfur battery positive electrode obtained in step (2) and the lithium negative electrode, separator and electrolyte obtained in step (3) are assembled to obtain a lithium-sulfur battery.

[0037] The beneficial effects of this invention are: This invention provides a method for preparing porous carbon materials modified with single-atom catalysts. Zn-MOF-RF particles are obtained by solvothermal method and phenolic resin coating, and then XN / HNPC composite materials modified with single-atom catalysts are prepared by solution impregnation method after adsorption of metal salts and high-temperature carbonization in an inert gas environment.

[0038] The single-atom catalyst-modified XN / HNPC composite material prepared in this invention exhibits excellent electrical conductivity, a large specific surface area, and a large pore structure, maximizing ion transport rate and sulfur utilization. Simultaneously, the introduction of a highly catalytically active single-atom catalyst increases the catalytically active sites in the composite material, enhancing the adsorption capacity of the cathode material for polysulfides, thereby improving the conversion kinetics of polysulfides during the electrochemical reaction, mitigating the shuttle effect of polysulfides, and reducing battery polarization. When the single-atom catalyst-modified XN / HNPC composite material is used as a lithium anode support, it can effectively regulate lithium-ion deposition and slow down the uncontrolled growth of lithium dendrites. Experimental results show that when the single-atom catalyst-modified XN / HNPC composite material is applied as both the cathode material and anode support in lithium-sulfur batteries, it can significantly improve the discharge capacity, rate performance, and cycle performance of lithium-sulfur batteries. The preparation method in this invention features mild reaction conditions and a simple process, providing guidance for the future commercial application of high-performance lithium-sulfur batteries. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the VN / HNPC material prepared in Example 1 of this invention. Figure 2Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the VN / HNPC material prepared in Example 1 of this invention; Figure 3 The nitrogen isothermal adsorption / desorption curve and pore size distribution diagram of the VN / HNPC material prepared in Example 1 of this invention; Figure 4 The image shows the X-ray absorption fine structure spectrum (XAFS) of the VN / HNPC material prepared in Example 1 of this invention. Figure 5 The above are data analysis diagrams of the binding energy of the materials prepared in Examples 1-5 of this invention to Li2S6. Figure 6 Performance diagrams of symmetrical batteries assembled on the negative electrode side of lithium-sulfur batteries using materials prepared in Examples 1 and 2 and Comparative Example 1 of this invention; Figure 7 The graph shows a comparison of the cycle performance of Application Example 1, Application Example 2 and Application Example 3 of the present invention when applied to lithium-sulfur batteries at 0.5 C. Figure 8 The cycling performance of the materials prepared in Examples 1 and 2 and Comparative Example 1 of the present invention as both positive and negative electrode carrier materials in lithium-sulfur batteries at a current density of 1 C is shown in the diagram. The obtained XRD pattern has the following parameters: x-axis represents the diffraction angle (2θ), and y-axis represents the diffraction peak intensity. The obtained nitrogen isothermal adsorption-desorption curve has the following parameters: x-axis represents the relative pressure, and y-axis represents the nitrogen adsorbed amount. The obtained X-ray absorption fine structure spectrum (XAFS) has the following parameters: x-axis represents the absorbed energy, and y-axis represents the absorbed intensity. The obtained symmetric cell performance graph has the following parameters: x-axis represents time, and y-axis represents voltage. The obtained cycle performance graph has the following parameters: x-axis represents the number of cycles, and y-axis represents the specific capacity. Detailed Implementation

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

[0042] Example 1 The preparation method of the VN / HNPC composite material modified with a single-atom catalyst in this embodiment is as follows: I. Preparation of Zinc-based Metal-Organic Framework Material ZIF-8 Nanoparticles First, 4 mg of hexadecyltrimethylammonium bromide (CTAB) was uniformly dispersed in 10 mL of deionized water. Then, 295 mg of zinc nitrate (Zn(NO3)26H2O) was added to the above solution and mixed thoroughly to obtain mixed solution A. Next, 4.54 g of 2-methylimidazole (C4H6N2) was added to another 70 mL of deionized water to obtain mixed solution B. After both mixed solutions were completely dissolved, mixed solution B was added to mixed solution A under rapid stirring. The mixture was magnetically stirred at room temperature for 40 min. The precipitate was collected by centrifugation at 5000 r / min for 5 min. Finally, the precipitate was washed three times or more with ethanol solution and dried in a vacuum oven at 60 ℃ for 6 hours to obtain ZIF-8 nanoparticles.

[0043] II. Coating ZIF-8 nanoparticles with phenolic resin (RF) to obtain ZIF-8-RF particles. First, 15 mg of resorcinol (C6H6O2), 15 mg of hexadecyltrimethylammonium bromide (CTAB), and 2.75 mL of formaldehyde solution were dissolved in 60 mL of deionized water. After stirring for 30 min, 200 mg of ZIF-8 nanoparticle precursor was added, and the mixture was sonicated for 10 min to ensure uniform dispersion. The mixture was then magnetically stirred at room temperature for 24 hours. The precipitate was collected by centrifugation at 5000 r / min for 5 min. Finally, the precipitate was washed with deionized water and dried in a vacuum oven at 60 °C for 6 hours to obtain ZIF-8-RF particles.

[0044] III. Uniformly loading V metal salt onto ZIF-8-RF particles using a solution impregnation method. 11 mg of vanadium diacetylacetonate (C 10 H 14 (O5V) was dispersed in 40 mL of ethanol solution. Then, 200 mg of ZIF-8-RF particles were weighed and uniformly dispersed in the above mixed solution. After magnetic stirring at room temperature for 24 hours, the precipitate was collected by centrifugation and washed 2-3 times with ethanol solution. Finally, it was placed in a vacuum oven and dried at 60 °C for 6 hours to obtain V metal salt-loaded ZIF-8-RF particles. The mass ratio of V to ZIF-8-RF was 1:100.

[0045] IV. Preparation of VN / HNPC composite materials modified with V single atoms and exhibiting high catalytic activity The V metal salt-loaded ZIF-8-RF particles obtained in step 3 were added to a ceramic boat and placed in a tube furnace. The furnace was heated to 900 °C at a rate of 5 °C / min under an argon atmosphere, held for 5 hours, and then cooled to room temperature. The collected black powder material is the V single-atom modified VN / HNPC composite material.

[0046] The XRD pattern of the highly catalytically active V single-atom modified VN / HNPC composite material prepared in this embodiment is shown in the figure below. Figure 1 As shown, the scanning electron microscope (SEM) and transmission electron microscope (TEM) images are as follows: Figure 2 As shown, the nitrogen isothermal adsorption-desorption curves and pore size distribution are as follows: Figure 3 As shown, the X-ray absorption fine structure spectrum is as follows: Figure 4 As shown. From Figure 1 It can be seen that the composite material only shows characteristic peaks belonging to graphitic carbon, indicating that no metal particles or clusters are formed in the composite material; from Figure 2 It can be seen that the composite material has a uniform cubic structure with particle sizes of approximately 200-300 nm, and the carbon material has a hollow structure; from Figure 3 It can be seen that the composite material has a large specific surface area (487.7870 m²). 2 / g); from Figure 4 It can be seen that V exists in the composite material in the form of a single atom and the coordination form is a V-N4 structure.

[0047] Example 2 This embodiment describes the preparation of Ni-N / HNPC composite material modified with Ni single atoms and its performance testing in lithium-sulfur batteries.

[0048] Unlike Example 1, in Example 2, the preparation process of ZIF-8 and ZIF-8-RF particles in the Ni-N / HNPC composite material with Ni single atom modification is the same as that in Example 1, and ZIF-8-RF particles are obtained.

[0049] I. Adsorption of Ni metal salt onto ZIF-8-RF particles via solution impregnation method 9 mg of nickel acetate (Ni(CH3COO)2·4(H2O)) was dissolved in 40 mL of ethanol solution. 200 mg of ZIF-8-RF particles were added while stirring. After stirring for 24 hours, the precipitate was collected by centrifugation. Finally, the precipitate was washed three times with ethanol solution and transferred to a vacuum oven to dry at 60 °C for 12 hours to obtain ZIF-8-RF particles adsorbed by Ni metal salt.

[0050] II. Preparation of Ni-N / HNPC composite materials modified with Ni single atoms The Ni metal salt-loaded ZIF-8-RF particles obtained in step one were added to a ceramic boat and placed in a tube furnace. The temperature was increased to 900 °C at a rate of 5 °C / min under an argon atmosphere, held for 5 hours, and then cooled to room temperature. The collected black powder material is the Ni-N / HNPC composite material modified with Ni single atoms.

[0051] The binding energy of Ni atoms to Li2S6 is as follows: Figure 5 As shown.

[0052] Example 3 This example describes the preparation of a Co-N / HNPC composite material modified with a single Co atom: Unlike Example 1, the preparation process of ZIF-8 and ZIF-8-RF particles in the Co-N / HNPC composite material with Co single-atom modification in Example 3 is the same as that in Example 1, and ZIF-8-RF particles are obtained.

[0053] I. Adsorption of Co metal salt onto ZIF-8-RF particles via solution impregnation method 10 mg of cobalt nitrate hexahydrate (Co(NO3)2·6(H2O)) was weighed and dissolved in 40 mL of ethanol solution. 200 mg of ZIF-8-RF particles were added while stirring. After stirring for 24 hours, the precipitate was collected by centrifugation. Finally, the precipitate was washed three times with ethanol solution and transferred to a vacuum oven to dry at 60 °C for 12 hours to obtain ZIF-8-RF particles adsorbed by Co metal salt.

[0054] II. Preparation of Co-N / HNPC composite materials modified with Co single atoms The Ni metal salt-loaded ZIF-8-RF particles obtained in step one were added to a ceramic boat and placed in a tube furnace. The temperature was increased to 900 °C at a rate of 5 °C / min under an argon atmosphere, held for 5 hours, and then cooled to room temperature. The black powder material collected was the Co-N / HNPC composite material modified with a single Co atom.

[0055] The binding energy of Co atoms to Li2S6 is as follows Figure 5 As shown.

[0056] Example 4 This example describes the preparation of Fe-N / HNPC composite materials modified with Fe single atoms: Unlike Example 1, the preparation process of ZIF-8 and ZIF-8-RF particles in the Fe-N / HNPC composite material with Fe single-atom modification in Example 4 is the same as that in Example 1, and ZIF-8-RF particles are obtained.

[0057] I. Adsorption of Fe metal salts onto ZIF-8-RF particles via solution impregnation method 14 mg of ferric nitrate nonahydrate (Fe(NO3)3·9(H2O)) was weighed and dissolved in 40 mL of ethanol solution. 200 mg of ZIF-8-RF particles were added while stirring. After stirring for 24 hours, the precipitate was collected by centrifugation. Finally, the precipitate was washed three times with ethanol solution and transferred to a vacuum oven to dry at 60 °C for 12 hours to obtain ZIF-8-RF particles adsorbed by Fe metal salt.

[0058] II. Preparation of Fe-N / HNPC composite materials modified with Fe single atoms The Ni metal salt-loaded ZIF-8-RF particles obtained in step one were added to a ceramic boat and placed in a tube furnace. The temperature was increased to 900 °C at a rate of 5 °C / min under an argon atmosphere, held for 5 hours, and then cooled to room temperature. The black powder material collected was the Fe-N / HNPC composite material modified with Fe single atoms.

[0059] The binding energy of Fe atoms to Li2S6 is as follows Figure 5 As shown.

[0060] Example 5 This embodiment describes the preparation of a Mn-N / HNPC composite material modified with a single Mn atom: Unlike the examples, the preparation process of ZIF-8 and ZIF-8-RF particles in the preparation of the Mn-N / HNPC composite material with Mn single-atom modification in Comparative Example 2 was the same as that in Example 1, resulting in ZIF-8-RF particles.

[0061] I. Adsorption of Mn metal salt onto ZIF-8-RF particles via solution impregnation method 9 mg of manganese acetate tetrahydrate (Mn(CH3COO)2·4(H2O)) was weighed and dissolved in 40 mL of ethanol solution. 200 mg of ZIF-8-RF particles were added under stirring. After stirring for 24 hours, the precipitate was collected by centrifugation. Finally, the precipitate was washed three times with ethanol solution and transferred to a vacuum oven to dry at 60 °C for 12 hours to obtain ZIF-8-RF particles adsorbed by Mn metal salt.

[0062] II. Preparation of Mn-N / HNPC composite materials modified with Mn single atoms The Mn metal salt-loaded ZIF-8-RF particles obtained in step one were added to a ceramic boat and placed in a tube furnace. The temperature was increased to 900 °C at a rate of 5 °C / min under an argon atmosphere, held for 5 hours, and then cooled to room temperature. The collected black powder material is the Mn-N / HNPC composite material modified with Mn single atoms.

[0063] The binding energy of Mn atoms to Li2S6 is as follows Figure 5 As shown.

[0064] Application Example 1 In this application example, the VN / HNPC composite material prepared in Example 1 is used only as a sulfur-carrying material for the positive electrode in the field of lithium-sulfur batteries. The specific steps are as follows: Sublimed sulfur and VN / HNPC composite material in a mass ratio of 7:3 were weighed and placed in a mortar, and ground thoroughly to ensure uniform mixing. The mixture was then placed in a glass tube and evacuated using a vacuum pump until the vacuum level reached below 10 mbar, which was maintained for 10 minutes. The tube was then sealed using an acetylene torch. The sealed glass tube was placed in an oven at 155 °C for 12 hours, and after cooling, the sulfur / VN / HNPC composite material was obtained.

[0065] The obtained sulfur / VN / HNPC composite material, Super P, and PVDF were mixed in a mass ratio of 8:1:1, using N-methylpyrrolidone (NMP) as the solvent. The mixture was ball-milled at 350 r / min for 2 hours to form a homogeneous slurry. The homogeneous slurry was then uniformly coated onto a carbon-coated aluminum foil current collector using a coater, and subsequently dried in a vacuum oven at 60 °C for 12 hours. The coater blade height was 400 μm, and the resulting electrode had a sulfur loading of 1 mg / cm³. 2 .

[0066] The prepared positive electrode was cut into 12 mm diameter sheets as the positive electrode, and a lithium sheet was used as the negative electrode. A polypropylene membrane (Celgard 2400) was used as the separator. An electrolyte containing 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) lithium salt and 1% lithium nitrate in a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) solvent (volume ratio 1:1) was added to assemble a coin cell. The battery was subjected to cycle performance testing, with a test voltage range of 1.7~2.8 V.

[0067] The binding energy of V atom to Li2S6 is as follows Figure 5 As shown. The battery cycle performance at 0.5 C with the VN / HNPC composite material used only as the positive electrode carrier is as follows. Figure 7 As shown.

[0068] Application Example 2 This application example uses the VN / HNPC composite material prepared in Example 1 as a negative electrode carrier material in a lithium-sulfur battery. The specific steps are as follows: VN / HNPC composite material, Super P, and PVDF were mixed uniformly at a mass ratio of 8:1:1, using N-methylpyrrolidone (NMP) as solvent, and a slurry was prepared by ball milling. The slurry was then coated onto a copper foil current collector using a coater and dried in a vacuum oven at 60°C for 12 hours. The coater blade height was 400 μm, and the coating surface density was 1 mg / cm³. 2 .

[0069] The copper foil coated with VN / HNPC obtained above was cut into 12 mm diameter electrodes as electrodes, and a lithium sheet was used as the counter electrode. A polypropylene membrane (Celgard 2400) was used as the separator. A coin cell was assembled using an electrolyte containing 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) lithium salt and 1% lithium nitrate in a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) solvent (volume ratio 1:1). Symmetrical battery cycle performance test: the current density for the first three cycles was 0.2 mA / cm². 2 Activation was performed by charge-discharge cycle between 0 and 1 V. Subsequent activation was carried out at 0.2 mA / cm². 2 Pre-deposition current density 5 mAh / cm 2 Lithium, then using 1 mA / cm 2 Current density, 1 mAh / cm 2 Cyclic performance tests were conducted on the capacity of the VN / HNPC composite material as the negative electrode carrier. The symmetrical cell performance was as follows: Figure 6 As shown.

[0070] Negative electrode preparation: The current density for the first three turns is 0.2 mA / cm². 2 Activation was performed by charge-discharge cycle between 0 and 1 V, followed by a cycle of 0.2 mA / cm². 2 The current density was used to pre-plate Li onto VN / HNPC, with a lithium content of 15 mAh / cm³. 2 The pre-lithium-plated electrode is removed and used as the negative electrode.

[0071] The positive electrode uses commercially available carbon nanotubes as the sulfur carrier material, and a polypropylene membrane (Celgard 2400) is used as the separator. An electrolyte containing 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1% lithium nitrate in a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) solvent (volume ratio 1:1) is added to assemble a coin cell. Cycle performance tests were conducted on the battery, with a test voltage range of 1.7–2.8 V.

[0072] The battery cycle performance at 0.5 C when the VN / HNPC composite material is used only as the negative electrode carrier is as follows: Figure 7 As shown.

[0073] Application Example 3 In this application example, the VN / HNPC composite material prepared in Example 1 is used simultaneously as both a positive electrode sulfur-carrying material and a negative electrode carrier material in a lithium-sulfur battery. The specific steps are as follows: The preparation process of VN / HNPC composite material as a positive electrode sulfur carrier is the same as in application example 1; the preparation process of VN / HNPC composite material as a negative electrode carrier is the same as in application example 2.

[0074] The prepared positive electrode was cut into 12 mm diameter sheets to serve as the positive electrode, and the pre-lithium-plated electrode was removed to serve as the negative electrode. A polypropylene membrane (Celgard 2400) was used as the separator, and an electrolyte containing 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) lithium salt and 1% lithium nitrate in a 1,3-dioxolane (DOL) / ethylene glycol dimethyl ether (DME) solvent (volume ratio 1:1) was added to assemble a coin cell. The battery was subjected to cycle performance testing, with a test voltage range of 1.7~2.8 V.

[0075] When VN / HNPC composite materials are used as both positive and negative electrode carriers in lithium-sulfur batteries, the cycle performance at a current rate of 0.5 C is as follows: Figure 7 As shown, the cycling performance at 1 C is as follows: Figure 8 As shown.

[0076] like Figure 7 The cycling performance of the VN / HNPC composite material as both positive and negative electrode carriers in lithium-sulfur batteries, and as coin cells assembled using both as positive and negative electrode carriers, shows that the positive electrode material has a significant impact on battery cycling performance. Without negative electrode modification, the S@VN / HNPC||Li coin cell exhibits a capacity decay of 607.9 mAh / g after 200 cycles. However, when the VN / HNPC composite material is used as both positive and negative electrode carriers, the S@VN / HNPC||Li@VN / HNPC coin cell retains a capacity of 862.2 mAh / g after 200 cycles. Therefore, negative electrode modification of VN / HNPC significantly improves the cycling capacity and reduces the capacity decay rate.

[0077] Application Example 4 In this application example, the Ni-N / HNPC composite material prepared in Example 2 is used as both a positive electrode sulfur carrier material and a negative electrode carrier material in a lithium-sulfur battery.

[0078] The steps of using Ni-N / HNPC composite material as a positive electrode carrier material, including sulfur loading process, preparation of positive electrode sheet, lithium-sulfur battery assembly, and using Ni-N / HNPC composite material as a negative electrode carrier material, preparation of negative electrode sheet, and testing, are the same as in Application Example 3.

[0079] Ni-N / HNPC composite material as a negative electrode carrier for assembling symmetrical batteries exhibits performance such as Figure 6 As shown, when Ni-N / HNPC composite material is used as both positive and negative electrode carrier material in lithium-sulfur batteries, the cycling performance at 1 C rate is as follows: Figure 8 As shown.

[0080] Comparative Example 1 Preparation of carbon materials (HNPC) without metal single atoms and performance testing of their application in lithium-sulfur batteries.

[0081] Unlike Example 1, the preparation process of ZIF-8-RF particles in Comparative Example 1 is the first two steps of the preparation process in Example 1, resulting in ZIF-8-RF particles.

[0082] Preparation of nitrogen-doped carbon material without metal single atoms: ZIF-8-RF particles were added to a ceramic boat and placed in a tube furnace. The temperature was increased to 900 °C at a rate of 5 °C / min under an argon atmosphere, held for 5 hours, and then cooled to room temperature. The black powder material collected was the nitrogen-doped carbon material without metal single atoms.

[0083] Application Comparative Example 1 Nitrogen-doped carbon materials without metal single atoms, used as a negative electrode carrier, exhibit the following performance characteristics when assembling symmetrical cells: Figure 6 As shown.

[0084] Using nitrogen-doped carbon material without metal single atoms as the positive electrode carrier material, the sulfur loading process, positive electrode preparation, lithium-sulfur battery assembly, and using nitrogen-doped carbon material without metal single atoms as the negative electrode carrier material, the negative electrode preparation, and testing are the same as in Application Example 3. The cycling performance at 1 C current is as follows: Figure 8 As shown.

[0085] like Figure 5 The figure shows the binding energies of different metal single-atom catalysts to Li₂S₆, from... Figure 5 It can be concluded that V atoms have a stronger interaction with Li2S6 compared to other metal single atoms, making them more suitable as a catalytic material for lithium-sulfur batteries.

[0086] like Figure 6 The figures shown are symmetrical battery performance diagrams assembled using the materials prepared in Examples 1, 2, and 1 (corresponding to Application Example 2, Application Example 4, and Comparative Example 1, respectively) as negative electrode carriers. The performance at 1 mA / cm² is... 2 Current density, 1 mAh / cm 2 At the deposition capacity, Application Example 2 exhibits a smaller polarization voltage and more stable cycling compared to Application Example 4 and Application Comparative Example 1.

[0087] like Figure 8 The figures show the cycling performance of the materials prepared in Examples 1, 2, and 1 (and Comparative Example 1) as both positive and negative electrode carriers in lithium-sulfur batteries at a 1 C current density (corresponding to the cycling performance of Application Example 3, Application Example 4, and Comparative Example 1 at a 1 C rate, respectively). Application Example 3 showed a discharge capacity of 598.6 mAh / g after 200 cycles, while Application Example 4 and Comparative Example 1 showed discharge capacities of 422.8 mAh / g and 193.8 mAh / g, respectively. The discharge capacity and cycling stability of Application Example 3 were significantly higher than those of Application Example 4 and Comparative Example 1. This indicates that the VN / HNPC composite material can effectively improve electrochemical reaction kinetics and suppress the shuttle effect of polysulfides. It also slows down lithium dendrite growth and enhances battery stability.

[0088] Therefore, the experimental data show that the VN / HNPC composite material modified with a V single-atom catalyst exhibits better electrochemical performance when used as a positive and negative electrode support material in lithium-sulfur batteries. Thus, the application of the VN / HNPC composite material modified with a V single-atom catalyst proposed in this invention as a positive and negative electrode support material in lithium-sulfur batteries is feasible.

[0089] This invention provides a method for preparing a VN / HNPC composite material modified with a V single-atom catalyst. The V single atoms are uniformly distributed on a porous carbon framework, exhibiting high conductivity and high catalytic activity at the VN sites, while the V atoms possess good lithiophilicity. When applied to lithium-sulfur batteries, it demonstrates superior electrochemical performance, significantly improving discharge capacity and cycle stability. This invention provides a new method and approach to address problems such as shuttle effect, volume expansion, and lithium dendrite growth in lithium-sulfur batteries. Furthermore, the preparation method features mild reaction conditions and a simple process, showing promising application prospects.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a single-atom modified porous carbon material, characterized in that, Includes the following steps: (1) Preparation of zinc-based metal-organic framework (Zn-MOF) particles; (2) Zn-MOF-RF nanoparticles were obtained by coating Zn-MOF nanoparticles with phenolic resin; (3) The metal salt X was uniformly loaded onto Zn-MOF-RF nanoparticles by solution impregnation; (4) The material obtained in step (3) is carbonized at high temperature in an inert gas atmosphere to obtain a hollow porous carbon material XN / HNPC with high catalytic activity modified by a single atom X; In step (2), the phenolic resin (RF) coating is carried out by uniformly dispersing Zn-MOF nanoparticles in a mixed solution of resorcinol and formaldehyde, stirring magnetically at room temperature for 18-24 hours, collecting the precipitate by centrifugation or filtration, washing with deionized water and ethanol, and drying in a vacuum oven at 60 °C for 6-12 hours. The mass ratio of resorcinol to formaldehyde in the mixed solution is 1:150, and the mass ratio of resorcinol to Zn-MOF nanoparticles is 5:100-10:

100. In step (3), the solution impregnation method involves uniformly dispersing Zn-MOF-RF nanoparticles into a metal salt solution of X, stirring magnetically at room temperature for 12-24 hours, collecting the precipitate by centrifugation or filtration, washing with deionized water and ethanol, and drying in a vacuum oven at 60 ℃ for 6-12 hours. The metal element X in the metal salt solution is one or more transition metal elements, including nickel, cobalt, iron, manganese, and vanadium. The metal salt of X includes acetate, nitrate, chlorate, and chloride of metal X. The concentration of metal ions in the metal salt solution is 0.1-5 mg / mL, and the mass ratio of Zn-MOF-RF nanoparticles to metal ions in the metal salt solution is 100:0.5-100:

2. The inert gas in step (4) is nitrogen or argon, the high-temperature carbonization temperature is 900~1100 ℃, and the time is 2~5 hours.

2. The single-atom modified porous carbon material prepared by the method according to claim 1, characterized in that, Porous carbon, as a carbon-based support material, has a large specific surface area and abundant pore structure. The specific surface area of ​​the composite material is greater than 400 m2 / g, the particle size is 200 nm~2 μm, and it has abundant micropore and mesopore structure. The mass fraction of carbon-based support material is 98%~99.9%, and the mass fraction of single-atom catalyst is 0.1%~2%.

3. A lithium-sulfur battery, characterized in that: The positive and / or negative electrodes of the lithium-sulfur battery contain the single-atom modified porous carbon material as described in claim 2.

4. The application of the single-atom modified porous carbon material according to claim 2 in lithium-sulfur batteries, characterized in that, The porous carbon material XN / HNPC modified with a single atom is used as the positive electrode sulfur loading material and / or negative electrode support material.

5. The application according to claim 4, characterized in that, The porous carbon material XN / HNPC modified with a single atom was used as the sulfur-supporting material in the positive electrode. The specific steps are as follows: 1) Sublimed sulfur and XN / HNPC composite material are uniformly mixed in a certain proportion, and sulfur / carbon composite cathode material is obtained by melt-filling sulfur under vacuum or inert gas atmosphere. The heating temperature is 155 ℃ and the holding time is 12~18 hours. The mass ratio of single-atom modified porous carbon material XN / HNPC in sulfur / carbon composite cathode material is 20%~50%. 2) The sulfur / carbon composite cathode material, conductive agent and binder obtained in step 1) are mixed in a certain proportion. Using N-methylpyrrolidone as solvent, the mixture is mixed evenly to form a slurry, which is then uniformly coated on the current collector. After vacuum drying, the lithium-sulfur battery cathode sheet is obtained. 3) Assemble the lithium-sulfur battery positive electrode, lithium negative electrode, separator, electrolyte and battery case obtained in step 2) into a lithium-sulfur battery.

6. The application according to claim 4, characterized in that, The single-atom modified porous carbon material XN / HNPC was used as an anode support material for lithium anode protection. The specific steps are as follows: (1) XN / HNPC composite material is mixed with conductive agent and binder in a certain proportion, and N-methylpyrrolidone is used as solvent. After being mixed evenly to form a slurry, it is coated on copper foil. The loading of XN / HNPC composite material on the copper foil surface is 0.5~0.8 mg / cm2. After vacuum drying, the copper foil modified with XN / HNPC composite material is used as the electrode, and the lithium sheet is used as the counter electrode. A certain capacity of lithium is deposited on the surface of the copper foil modified with XN / HNPC composite material to obtain the modified lithium anode. The specific preparation method is as follows: the current density for the first three cycles is 0.2 mA / cm2, and the charge and discharge activation is carried out between 0~1 V. After that, the current density is 0.2 mA / cm2. 2 The current density was used to pre-plate Li onto XN / HNPC with a lithium content of 15 mAh / cm2, and the pre-plated lithium electrode was removed and used as the negative electrode. (2) The modified lithium anode obtained in step (1) and the positive electrode, separator and electrolyte using commercially available carbon nanotubes as sulfur carrier materials are assembled to obtain a lithium-sulfur battery.

7. The application according to claim 4, characterized in that, The single-atom modified porous carbon material XN / HNPC is used as both a sulfur-carrying material in the positive electrode and a sulfur-supporting material in the negative electrode for lithium anode protection. The specific steps are as follows: (1) Sublimed sulfur and XN / HNPC composite material are uniformly mixed in a certain proportion, and sulfur / carbon composite cathode material is obtained by melt-filling sulfur under vacuum or inert gas atmosphere. The heating temperature is 155 ℃ and the holding time is 12~18 hours. The mass ratio of single-atom modified porous carbon material XN / HNPC in sulfur / carbon composite cathode material is 20%~50%. (2) The sulfur / carbon composite cathode material, conductive agent and binder obtained in step 1) are mixed in a certain proportion, and N-methylpyrrolidone is used as solvent. After being mixed evenly to form a slurry, it is uniformly coated on carbon-coated aluminum foil and vacuum dried to obtain the lithium-sulfur battery cathode sheet. (3) Mix the XN / HNPC composite material with a conductive agent and a binder in a certain proportion, use N-methylpyrrolidone as a solvent, mix evenly to form a slurry, coat it onto a copper foil, and dry it under vacuum to obtain a copper foil modified with XN / HNPC composite material as an electrode and a lithium sheet as a counter electrode. By depositing a certain capacity of lithium on the surface of the copper foil modified with XN / HNPC composite material, a modified lithium anode is obtained. (4) Assemble the lithium-sulfur battery positive electrode obtained in step (2) and the lithium negative electrode, separator and electrolyte obtained in step (3) into a lithium-sulfur battery.

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